feat: Complete tablet UI overhaul with popup menu system and help bubble

Major Changes:
- 🪟 Popup Menu System: Converted slide-down navigation to draggable, minimizable popup window
- ❓ Help Bubble: Added contextual help system for admin dashboard (accessible via ? bubble)
- 🎨 Universal Theme Engine: All elements now properly match selected theme across all panels
- 📱 Enhanced Tablet Support: Comprehensive touch gestures, handwriting recognition, and Apple Pencil optimization
- 🖊️ Unified Write Mode: Combined handwriting and keyboard input with large canvas interface

Technical Implementation:
- Draggable popup with minimize/restore functionality and boundary constraints
- Dynamic theme switching using CSS variables throughout all components
- Help system with modal overlay and keyboard shortcuts (ESC to close)
- Responsive design optimizations for mobile, tablet, and desktop
- Comprehensive CSS overrides to eliminate hardcoded colors
- JavaScript fixes for canvas stroke colors and input styling

UI/UX Improvements:
- Clean admin dashboard without instruction clutter
- Professional popup interface with smooth animations
- Better contrast and readability across all themes (default, playground, chalkboard, galaxy, nature)
- Improved accessibility with proper focus management
- Enhanced mobile responsiveness with touch-optimized controls

Files Modified:
- Menu system: tablet-menu.js, tablet-menu.css
- Theme engine: styles.css, themes integration
- Admin interface: index.html, ui.js
- Input systems: game.js, unified-write.js, handwriting.js
- Authentication: auth.js with tablet menu cleanup

public/js/auth.js

@@ -72,6 +72,14 @@ async function verifyLogin() {
 function logoutUser() {
   localStorage.removeItem('loggedInUser');
 
+  // Clear current user
+  window.currentUser = null;
+
+  // Close tablet menu if open
+  if (window.tabletMenuManager && window.tabletMenuManager.isMenuOpen()) {
+    window.tabletMenuManager.forceCloseMenu();
+  }
+
   // Hide all panels
   document.getElementById('adminPanel')?.classList.add('hidden');
   document.getElementById('studentPanel')?.classList.add('hidden');