fix: refactor contents control architecture and resolve resize handle positioning

- Streamlined ContentsControl to use base class generateContent pattern
- Removed duplicate methods and unified content generation approach
- Added overflow: visible to fix content visibility issues
- Fixed resize handle positioning (moved from -4px to 1px/2px from right edge)
- Improved search functionality to properly rebuild content
- Enhanced refresh button detection to prevent conflicts
- Removed unused getDocumentStats method and duplicate code blocks

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

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

testdrive-jsui/static/js/controls/control-base.js

@@ -541,7 +541,7 @@ class ControlBase {
         resizeHandle.style.cssText = `
             position: absolute;
             bottom: 0px;
-            right: -4px;
+            right: 2px;
             width: 12px;
             height: 12px;
             cursor: se-resize;