feat: improve remove background with edge smoothing, color decontamination, output formats

- Expose birefnet-hr-matting in UI (People/Ultra) and fix model defaults
  (People/Max now uses birefnet-matting for true alpha matting)
- Add output format selector (PNG/WebP/AVIF) with lossless alpha support
- Add edge smoothing post-processing (Off/Light/Medium/Strong) via
  morphological mask refinement to reduce gray halo artifacts
- Add color decontamination to remove background color spill from
  semi-transparent edge pixels
- Thread new settings through full stack: frontend -> API schema ->
  Python sidecar -> Sharp effects pipeline
- Add i18n keys for all 21 locales
- Add unit tests for new option serialization (3 tests)
- Add integration tests for new settings validation (4 tests)

packages/shared/src/i18n/ar.ts

@@ -587,6 +587,13 @@ export const ar: TranslationKeys = {
       intensity: "الشدة",
       addShadow: "إضافة ظل",
       opacity: "الشفافية",
+      outputFormat: "Output Format",
+      edgeSmoothing: "Edge Smoothing",
+      edgeSmoothingOff: "Off",
+      edgeSmoothingLight: "Light",
+      edgeSmoothingMedium: "Medium",
+      edgeSmoothingStrong: "Strong",
+      colorDecontamination: "Color Decontamination",
       rendering: "جاري المعالجة...",
       submit: "إزالة الخلفية",
       submitBatch: "إزالة الخلفية ({count} ملف)",

packages/shared/src/i18n/de.ts

@@ -595,6 +595,13 @@ export const de: TranslationKeys = {
       intensity: "Intensitaet",
       addShadow: "Schatten hinzufuegen",
       opacity: "Deckkraft",
+      outputFormat: "Output Format",
+      edgeSmoothing: "Edge Smoothing",
+      edgeSmoothingOff: "Off",
+      edgeSmoothingLight: "Light",
+      edgeSmoothingMedium: "Medium",
+      edgeSmoothingStrong: "Strong",
+      colorDecontamination: "Color Decontamination",
       rendering: "Wird gerendert...",
       submit: "Hintergrund entfernen",
       submitBatch: "Hintergrund entfernen ({count} Dateien)",

packages/shared/src/i18n/en.ts

@@ -545,6 +545,13 @@ export const en = {
       intensity: "Intensity",
       addShadow: "Add Shadow",
       opacity: "Opacity",
+      outputFormat: "Output Format",
+      edgeSmoothing: "Edge Smoothing",
+      edgeSmoothingOff: "Off",
+      edgeSmoothingLight: "Light",
+      edgeSmoothingMedium: "Medium",
+      edgeSmoothingStrong: "Strong",
+      colorDecontamination: "Color Decontamination",
       rendering: "Rendering...",
       submit: "Remove Background",
       submitBatch: "Remove Background ({count} files)",

packages/shared/src/i18n/es.ts

@@ -579,6 +579,13 @@ export const es: TranslationKeys = {
       intensity: "Intensidad",
       addShadow: "Agregar sombra",
       opacity: "Opacidad",
+      outputFormat: "Output Format",
+      edgeSmoothing: "Edge Smoothing",
+      edgeSmoothingOff: "Off",
+      edgeSmoothingLight: "Light",
+      edgeSmoothingMedium: "Medium",
+      edgeSmoothingStrong: "Strong",
+      colorDecontamination: "Color Decontamination",
       rendering: "Renderizando...",
       submit: "Eliminar fondo",
       submitBatch: "Eliminar fondo ({count} archivos)",

packages/shared/src/i18n/fr.ts

@@ -596,6 +596,13 @@ export const fr: TranslationKeys = {
       intensity: "Intensite",
       addShadow: "Ajouter une ombre",
       opacity: "Opacite",
+      outputFormat: "Output Format",
+      edgeSmoothing: "Edge Smoothing",
+      edgeSmoothingOff: "Off",
+      edgeSmoothingLight: "Light",
+      edgeSmoothingMedium: "Medium",
+      edgeSmoothingStrong: "Strong",
+      colorDecontamination: "Color Decontamination",
       rendering: "Rendu en cours...",
       submit: "Supprimer l'arriere-plan",
       submitBatch: "Supprimer l'arriere-plan ({count} fichiers)",

packages/shared/src/i18n/hi.ts

@@ -583,6 +583,13 @@ export const hi: TranslationKeys = {
       intensity: "तीव्रता",
       addShadow: "शैडो जोड़ें",
       opacity: "ओपेसिटी",
+      outputFormat: "Output Format",
+      edgeSmoothing: "Edge Smoothing",
+      edgeSmoothingOff: "Off",
+      edgeSmoothingLight: "Light",
+      edgeSmoothingMedium: "Medium",
+      edgeSmoothingStrong: "Strong",
+      colorDecontamination: "Color Decontamination",
       rendering: "रेंडर हो रहा है...",
       submit: "बैकग्राउंड हटाएं",
       submitBatch: "बैकग्राउंड हटाएं ({count} फाइलें)",

packages/shared/src/i18n/id.ts

@@ -593,6 +593,13 @@ export const id: TranslationKeys = {
       intensity: "Intensitas",
       addShadow: "Tambah Bayangan",
       opacity: "Opasitas",
+      outputFormat: "Output Format",
+      edgeSmoothing: "Edge Smoothing",
+      edgeSmoothingOff: "Off",
+      edgeSmoothingLight: "Light",
+      edgeSmoothingMedium: "Medium",
+      edgeSmoothingStrong: "Strong",
+      colorDecontamination: "Color Decontamination",
       rendering: "Merender...",
       submit: "Hapus Latar Belakang",
       submitBatch: "Hapus Latar Belakang ({count} file)",

packages/shared/src/i18n/it.ts

@@ -592,6 +592,13 @@ export const it: TranslationKeys = {
       intensity: "Intensita",
       addShadow: "Aggiungi ombra",
       opacity: "Opacita",
+      outputFormat: "Output Format",
+      edgeSmoothing: "Edge Smoothing",
+      edgeSmoothingOff: "Off",
+      edgeSmoothingLight: "Light",
+      edgeSmoothingMedium: "Medium",
+      edgeSmoothingStrong: "Strong",
+      colorDecontamination: "Color Decontamination",
       rendering: "Rendering...",
       submit: "Rimuovi sfondo",
       submitBatch: "Rimuovi sfondo ({count} file)",

packages/shared/src/i18n/ja.ts

@@ -552,6 +552,13 @@ export const ja: TranslationKeys = {
       intensity: "強度",
       addShadow: "シャドウ追加",
       opacity: "不透明度",
+      outputFormat: "Output Format",
+      edgeSmoothing: "Edge Smoothing",
+      edgeSmoothingOff: "Off",
+      edgeSmoothingLight: "Light",
+      edgeSmoothingMedium: "Medium",
+      edgeSmoothingStrong: "Strong",
+      colorDecontamination: "Color Decontamination",
       rendering: "レンダリング中...",
       submit: "背景を除去",
       submitBatch: "背景を除去（{count}ファイル）",

packages/shared/src/i18n/ko.ts

@@ -539,6 +539,13 @@ export const ko: TranslationKeys = {
       intensity: "강도",
       addShadow: "그림자 추가",
       opacity: "불투명도",
+      outputFormat: "Output Format",
+      edgeSmoothing: "Edge Smoothing",
+      edgeSmoothingOff: "Off",
+      edgeSmoothingLight: "Light",
+      edgeSmoothingMedium: "Medium",
+      edgeSmoothingStrong: "Strong",
+      colorDecontamination: "Color Decontamination",
       rendering: "렌더링 중...",
       submit: "배경 제거",
       submitBatch: "배경 제거 ({count}개 파일)",

packages/shared/src/i18n/nl.ts

@@ -593,6 +593,13 @@ export const nl: TranslationKeys = {
       intensity: "Intensiteit",
       addShadow: "Schaduw toevoegen",
       opacity: "Dekking",
+      outputFormat: "Output Format",
+      edgeSmoothing: "Edge Smoothing",
+      edgeSmoothingOff: "Off",
+      edgeSmoothingLight: "Light",
+      edgeSmoothingMedium: "Medium",
+      edgeSmoothingStrong: "Strong",
+      colorDecontamination: "Color Decontamination",
       rendering: "Renderen...",
       submit: "Achtergrond verwijderen",
       submitBatch: "Achtergrond verwijderen ({count} bestanden)",

packages/shared/src/i18n/pl.ts

@@ -596,6 +596,13 @@ export const pl: TranslationKeys = {
       intensity: "Intensywność",
       addShadow: "Dodaj cień",
       opacity: "Krycie",
+      outputFormat: "Output Format",
+      edgeSmoothing: "Edge Smoothing",
+      edgeSmoothingOff: "Off",
+      edgeSmoothingLight: "Light",
+      edgeSmoothingMedium: "Medium",
+      edgeSmoothingStrong: "Strong",
+      colorDecontamination: "Color Decontamination",
       rendering: "Renderowanie...",
       submit: "Usuń tło",
       submitBatch: "Usuń tło ({count} plików)",

packages/shared/src/i18n/pt-BR.ts

@@ -592,6 +592,13 @@ export const ptBR: TranslationKeys = {
       intensity: "Intensidade",
       addShadow: "Adicionar sombra",
       opacity: "Opacidade",
+      outputFormat: "Output Format",
+      edgeSmoothing: "Edge Smoothing",
+      edgeSmoothingOff: "Off",
+      edgeSmoothingLight: "Light",
+      edgeSmoothingMedium: "Medium",
+      edgeSmoothingStrong: "Strong",
+      colorDecontamination: "Color Decontamination",
       rendering: "Renderizando...",
       submit: "Remover fundo",
       submitBatch: "Remover fundo ({count} arquivos)",

packages/shared/src/i18n/ru.ts

@@ -594,6 +594,13 @@ export const ru: TranslationKeys = {
       intensity: "Интенсивность",
       addShadow: "Добавить тень",
       opacity: "Непрозрачность",
+      outputFormat: "Output Format",
+      edgeSmoothing: "Edge Smoothing",
+      edgeSmoothingOff: "Off",
+      edgeSmoothingLight: "Light",
+      edgeSmoothingMedium: "Medium",
+      edgeSmoothingStrong: "Strong",
+      colorDecontamination: "Color Decontamination",
       rendering: "Рендеринг...",
       submit: "Удалить фон",
       submitBatch: "Удалить фон ({count} файлов)",

packages/shared/src/i18n/sv.ts

@@ -591,6 +591,13 @@ export const sv: TranslationKeys = {
       intensity: "Intensitet",
       addShadow: "Lagg till skugga",
       opacity: "Opacitet",
+      outputFormat: "Output Format",
+      edgeSmoothing: "Edge Smoothing",
+      edgeSmoothingOff: "Off",
+      edgeSmoothingLight: "Light",
+      edgeSmoothingMedium: "Medium",
+      edgeSmoothingStrong: "Strong",
+      colorDecontamination: "Color Decontamination",
       rendering: "Renderar...",
       submit: "Ta bort bakgrund",
       submitBatch: "Ta bort bakgrund ({count} filer)",

packages/shared/src/i18n/th.ts

@@ -583,6 +583,13 @@ export const th: TranslationKeys = {
       intensity: "ความเข้ม",
       addShadow: "เพิ่มเงา",
       opacity: "ความทึบ",
+      outputFormat: "Output Format",
+      edgeSmoothing: "Edge Smoothing",
+      edgeSmoothingOff: "Off",
+      edgeSmoothingLight: "Light",
+      edgeSmoothingMedium: "Medium",
+      edgeSmoothingStrong: "Strong",
+      colorDecontamination: "Color Decontamination",
       rendering: "กำลังเรนเดอร์...",
       submit: "ลบพื้นหลัง",
       submitBatch: "ลบพื้นหลัง ({count} ไฟล์)",

packages/shared/src/i18n/tr.ts

@@ -595,6 +595,13 @@ export const tr: TranslationKeys = {
       intensity: "Yoğunluk",
       addShadow: "Gölge Ekle",
       opacity: "Opaklık",
+      outputFormat: "Output Format",
+      edgeSmoothing: "Edge Smoothing",
+      edgeSmoothingOff: "Off",
+      edgeSmoothingLight: "Light",
+      edgeSmoothingMedium: "Medium",
+      edgeSmoothingStrong: "Strong",
+      colorDecontamination: "Color Decontamination",
       rendering: "İşleniyor...",
       submit: "Arka Planı Kaldır",
       submitBatch: "Arka Planı Kaldır ({count} dosya)",

packages/shared/src/i18n/uk.ts

@@ -594,6 +594,13 @@ export const uk: TranslationKeys = {
       intensity: "Інтенсивність",
       addShadow: "Додати тінь",
       opacity: "Непрозорість",
+      outputFormat: "Output Format",
+      edgeSmoothing: "Edge Smoothing",
+      edgeSmoothingOff: "Off",
+      edgeSmoothingLight: "Light",
+      edgeSmoothingMedium: "Medium",
+      edgeSmoothingStrong: "Strong",
+      colorDecontamination: "Color Decontamination",
       rendering: "Рендеринг...",
       submit: "Видалити фон",
       submitBatch: "Видалити фон ({count} файлів)",

packages/shared/src/i18n/vi.ts

@@ -594,6 +594,13 @@ export const vi: TranslationKeys = {
       intensity: "Cường độ",
       addShadow: "Thêm bóng đổ",
       opacity: "Độ mờ",
+      outputFormat: "Output Format",
+      edgeSmoothing: "Edge Smoothing",
+      edgeSmoothingOff: "Off",
+      edgeSmoothingLight: "Light",
+      edgeSmoothingMedium: "Medium",
+      edgeSmoothingStrong: "Strong",
+      colorDecontamination: "Color Decontamination",
       rendering: "Đang kết xuất...",
       submit: "Xóa nền",
       submitBatch: "Xóa nền ({count} tệp)",

packages/shared/src/i18n/zh-CN.ts

@@ -537,6 +537,13 @@ export const zhCN: TranslationKeys = {
       intensity: "强度",
       addShadow: "添加阴影",
       opacity: "不透明度",
+      outputFormat: "Output Format",
+      edgeSmoothing: "Edge Smoothing",
+      edgeSmoothingOff: "Off",
+      edgeSmoothingLight: "Light",
+      edgeSmoothingMedium: "Medium",
+      edgeSmoothingStrong: "Strong",
+      colorDecontamination: "Color Decontamination",
       rendering: "渲染中...",
       submit: "移除背景",
       submitBatch: "移除背景（{count} 个文件）",

packages/shared/src/i18n/zh-TW.ts

@@ -536,6 +536,13 @@ export const zhTW: TranslationKeys = {
       intensity: "強度",
       addShadow: "加入陰影",
       opacity: "不透明度",
+      outputFormat: "Output Format",
+      edgeSmoothing: "Edge Smoothing",
+      edgeSmoothingOff: "Off",
+      edgeSmoothingLight: "Light",
+      edgeSmoothingMedium: "Medium",
+      edgeSmoothingStrong: "Strong",
+      colorDecontamination: "Color Decontamination",
       rendering: "算繪中...",
       submit: "移除背景",
       submitBatch: "移除背景（{count}個檔案）",