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/lib/tool-i18n.ts

@@ -0,0 +1,15 @@
+import type { TranslationKeys } from "@snapotter/shared";
+
+export function getToolName(t: TranslationKeys, toolId: string, fallback: string): string {
+  const entry = (t.tools as Record<string, { name?: string }>)[toolId];
+  return entry?.name ?? fallback;
+}
+
+export function getToolDescription(t: TranslationKeys, toolId: string, fallback: string): string {
+  const entry = (t.tools as Record<string, { description?: string }>)[toolId];
+  return entry?.description ?? fallback;
+}
+
+export function getCategoryName(t: TranslationKeys, categoryId: string, fallback: string): string {
+  return (t.categories as Record<string, string>)[categoryId] ?? fallback;
+}