feat(i18n): 21-language pipeline, landing/docs/API wiring, landing+API translations

Shared Claude Code translation pipeline (scripts/i18n, no API key) plus Astro/VitePress/Scalar i18n wiring. Landing and API reference translated into all 20 languages; docs i18n wiring + English source anchors. The translated docs markdown (apps/docs/<locale>/**, 3,620 files) follows in a companion PR because it exceeds GitHub's per-PR CI file limit.

scripts/i18n/lib/glossary.mjs

@@ -0,0 +1,61 @@
+// scripts/i18n/lib/glossary.mjs
+import { SUPPORTED_LOCALES } from "../../../packages/shared/src/i18n/index.ts";
+
+/** Terms that must stay verbatim in every language. */
+export const DO_NOT_TRANSLATE = [
+  "SnapOtter",
+  "API",
+  "REST",
+  "JSON",
+  "YAML",
+  "URL",
+  "HTTP",
+  "JPEG",
+  "PNG",
+  "WebP",
+  "AVIF",
+  "HEIC",
+  "GIF",
+  "SVG",
+  "EXIF",
+  "PDF",
+  "FFmpeg",
+  "Docker",
+  "Compose",
+  "Postgres",
+  "Redis",
+  "OIDC",
+  "SSO",
+  "SAML",
+  "SCIM",
+];
+
+/**
+ * @param {string} locale
+ * @returns {string} the English display name of the locale
+ */
+function localeName(locale) {
+  const entry = SUPPORTED_LOCALES.find((l) => l.code === locale);
+  if (!entry) throw new Error(`Unknown locale: ${locale}`);
+  return entry.name;
+}
+
+/**
+ * System prompt for translating one batch into `locale`.
+ * @param {string} locale
+ * @returns {string}
+ */
+export function buildSystemPrompt(locale) {
+  const name = localeName(locale);
+  return [
+    `You are a professional software-localization translator. Translate the user's content into ${name}.`,
+    "",
+    "Rules:",
+    `- Translate prose only. Preserve all markdown structure, whitespace, and line breaks exactly.`,
+    `- Never translate, reorder, or remove any ⸤I18N…⸥ marker. Copy each one verbatim in place.`,
+    `- Do not translate these terms; keep them exactly as written: ${DO_NOT_TRANSLATE.join(", ")}.`,
+    `- Keep code, URLs, file paths, and CLI flags unchanged.`,
+    `- Preserve the meaning and tone. Do not add notes, explanations, or extra text.`,
+    `- Output only the translation. No preamble, no closing remarks.`,
+  ].join("\n");
+}