Fixed remaining language persistence issues where sidebar and hero section
did not update when switching languages via navbar flags.
**Changes:**
- languageChanged event now calls updatePageUI() to update hero section
- languageChanged event now calls loadDocuments() to reload sidebar
- All UI elements update immediately without requiring page refresh
**Updated Elements on Language Change:**
- Hero section (page title, subtitle, search button)
- Sidebar category labels (Getting Started, Resources, etc.)
- Sidebar document titles (shows translations if available)
- Document content (reloads in new language)
- GitHub section links
**Result:**
✅ Click language flag → entire page switches instantly
✅ No page refresh required
✅ All UI elements synchronized
✅ Ready for Caixin Global launch (Oct 29)
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
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