fix: explorer toggle button hidden behind main content

The collapse/expand toggle button on the explorer panel was being
rendered behind the main editor area due to missing stacking context
and overflow clipping.

Changes to .ideResizeExplorer:
- Changed overflow from hidden to visible to allow the button to render
  outside container bounds
- Added position: relative and z-index: 10 to establish proper stacking
  context above the adjacent editor area

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

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

Author: tahierhussain

frontend/src/ide/ide-layout.css

@@ -36,8 +36,10 @@
 .ideResizeExplorer {
   background-color: var(--chat-ai-bg-color);
   transition: width 0.2s ease;
-  overflow: hidden;
+  overflow: visible;
   flex-shrink: 0;
+  position: relative;
+  z-index: 10;
 }
 
 .ideBody > .flex-1 {