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/components/markdown-content.tsx

@@ -1,5 +1,6 @@
 'use client'
 
+import { memo } from 'react'
 import ReactMarkdown from 'react-markdown'
 import remarkGfm from 'remark-gfm'
 import remarkMath from 'remark-math'
@@ -11,7 +12,7 @@ interface MarkdownContentProps {
   className?: string
 }
 
-export function MarkdownContent({ content, className = '' }: MarkdownContentProps) {
+export const MarkdownContent = memo(function MarkdownContent({ content, className }: MarkdownContentProps) {
   return (
     <div className={`prose prose-sm prose-compact dark:prose-invert max-w-none break-words ${className}`}>
       <ReactMarkdown
@@ -20,11 +21,11 @@ export function MarkdownContent({ content, className = '' }: MarkdownContentProp
         components={{
           a: ({ node, ...props }) => (
             <a {...props} className="text-primary hover:underline" target="_blank" rel="noopener noreferrer" />
-          )
+          ),
         }}
       >
         {content}
       </ReactMarkdown>
     </div>
   )
-}
+})