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/api/src/index.ts

@@ -23,6 +23,7 @@ import { analyticsRoutes } from "./routes/analytics.js";
 import { apiKeyRoutes } from "./routes/api-keys.js";
 import { auditLogRoutes } from "./routes/audit-log.js";
 import { registerBatchRoutes } from "./routes/batch.js";
+import { configRoutes } from "./routes/config.js";
 import { docsRoutes } from "./routes/docs.js";
 import { registerFeatureRoutes } from "./routes/features.js";
 import { registerFetchUrlsRoute } from "./routes/fetch-urls.js";
@@ -172,6 +173,9 @@ await app.register(cookie, {
   hook: "onRequest",
 });
 
+// Public config routes (no auth required)
+await configRoutes(app);
+
 // Auth middleware (must be registered before routes it protects)
 await authMiddleware(app);