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/app/(auth)/layout.tsx

@@ -8,7 +8,7 @@ export default function AuthLayout({
   children: React.ReactNode;
 }>) {
   return (
-    <LanguageProvider initialLanguage="fr">
+    <LanguageProvider>
       <div className="flex min-h-screen items-center justify-center bg-gray-50 dark:bg-zinc-950">
         <div className="w-full max-w-md p-4">
           {children}