feat: add multi-language support for 20 locales

Add complete i18n infrastructure with 21 supported languages:
English, Simplified Chinese, Traditional Chinese, Japanese, Korean,
Spanish, French, Italian, Brazilian Portuguese, German, Dutch, Swedish,
Russian, Polish, Ukrainian, Arabic (RTL), Turkish, Hindi, Vietnamese,
Indonesian, and Thai.

- I18nProvider context with three-tier locale detection
  (user preference > navigator.languages > instance default > English)
- ~1500 translation keys per locale with TypeScript-enforced completeness
- Dynamic code-splitting: only the active locale is loaded at runtime
- Language selectors in footer, login page, settings, and mobile sidebar
- Arabic RTL support with CSS logical properties across all components
- Tool names, descriptions, and categories translated via i18n helpers
- Public API endpoint GET /api/v1/config/locale for instance default
- Multi-script font stack (CJK, Arabic, Devanagari, Thai, Cyrillic)
- format() and plural() helpers for interpolation and pluralization
- API error translation mapping (translateApiError)
- 36 Playwright e2e tests verifying all 21 locales load correctly
- 25 unit tests for format, plural, locale detection, and completeness
- Updated translations.md docs and CLAUDE.md conventions

apps/web/src/components/tools/text-overlay-settings.tsx

@@ -1,7 +1,9 @@
 import { Download } from "lucide-react";
 import { useEffect, useRef, useState } from "react";
 import { ProgressCard } from "@/components/common/progress-card";
+import { useTranslation } from "@/contexts/i18n-context";
 import { useToolProcessor } from "@/hooks/use-tool-processor";
+import { format } from "@/lib/format";
 import { useFileStore } from "@/stores/file-store";
 
 export interface TextOverlayControlsProps {
@@ -155,6 +157,7 @@ export function TextOverlayControls({
 }
 
 export function TextOverlaySettings() {
+  const { t } = useTranslation();
   const { files } = useFileStore();
   const {
     processFiles,