feat: enhance control panel UI and resize functionality

Panel UI improvements:
- Replace heading elements (h1-h6) with styled divs to avoid navigation interference
- Change ContentsControl position from northwest to west for better accessibility

Panel collapse/expand enhancements:
- Fix panel dragging to prevent unexpected positioning jumps
- Keep panel width and upper-left position when collapsing to header-only mode
- Complete height reduction when collapsed (no minimal size maintained)
- Toggle resize handle visibility based on panel state

Resize handle improvements:
- Change resize symbol from arrow to clean dot (●) in bottom-right corner
- Remove background circle, show transparent dot only
- Fix resize direction to properly follow mouse movement from bottom-right
- Set dynamic minimum size constraints (header height + padding)
- Allow arbitrary panel sizing with proper bounds checking
- Reset panel size to defaults when closed/collapsed

🤖 Generated with [Claude Code](https://claude.ai/code)

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

markitect/static/js/main-updated.js

@@ -82,13 +82,13 @@ const MarkitectMain = {
     initializeControlPanels: function() {
         console.log('🎛️ Initializing enhanced control panels with compass positioning...');
 
-        // ContentsControl (Northwest)
+        // ContentsControl (West)
         if (typeof ContentsControl !== 'undefined') {
             this.contentsControl = new ContentsControl();
-            this.contentsControl.config.position = 'nw';
+            this.contentsControl.config.position = 'w';
             this.contentsControl.show();
             window.contentsControl = this.contentsControl;
-            console.log('✅ ContentsControl initialized (Northwest) with enhanced ControlBase');
+            console.log('✅ ContentsControl initialized (West) with enhanced ControlBase');
         }
 
         // StatusControl (East)