fix: i18n system overhaul and sidebar UI bugs

- Fix LanguageProvider: add RTL support (ar/fa), translation caching,
  prevent blank flash during load, browser language detection
- Fix detect-user-language: extend whitelist from 5 to all 15 languages
- Remove hardcoded initialLanguage="fr" from auth layout
- Complete fr.json translation (all sections translated from English)
- Add missing admin.ai keys to all 13 non-English locales
- Translate ai.autoLabels, ai.batchOrganization, memoryEcho sections
  for all locales
- Remove duplicate top-level autoLabels/batchOrganization from en.json
- Fix notebook creation: replace window.location.reload() with
  createNotebookOptimistic + router.refresh()
- Fix notebook name truncation in sidebar with min-w-0
- Remove redundant router.refresh() after note creation in page.tsx

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

keep-notes/lib/i18n/detect-user-language.ts

@@ -49,7 +49,7 @@ export async function detectUserLanguage(): Promise<SupportedLanguage> {
     if (sortedLanguages.length > 0) {
       const topLanguage = sortedLanguages[0][0] as SupportedLanguage
       // Verify it's a supported language
-      if (['fr', 'en', 'es', 'de', 'fa'].includes(topLanguage)) {
+      if (['en', 'fr', 'es', 'de', 'fa', 'it', 'pt', 'ru', 'zh', 'ja', 'ko', 'ar', 'hi', 'nl', 'pl'].includes(topLanguage)) {
         return topLanguage
       }
     }