fix: add status message element and fix column resizing bug

This commit fixes two bugs:

1. Issue #7: Missing status message DOM element
   - Added #status-message div to index.html
   - Added CSS styling with type-based classes (info, success, error)
   - Enhanced showMessage() to apply type classes for visual styling
   - Messages auto-hide after 3 seconds with fade-in animation

2. Column resizing visual bug:
   - Changed grid-template-columns from flexible (1fr 3fr 1fr)
   - To fixed minimum widths: minmax(200px, 250px) minmax(600px, 3fr) minmax(200px, 250px)
   - Prevents columns from resizing when content changes (captured pieces, move history)
   - Maintains stable layout throughout gameplay

Tests:
- Added status-message.test.js with 10 test cases
- Added column-resize.test.js with 8 test cases
- Tests verify DOM element existence, CSS styling, auto-hide behavior, and layout stability

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

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

js/main.js

@@ -245,6 +245,9 @@ class ChessApp {
             console.warn('Status message element not found, using console:', message);
             return;
         }
+
+        // Add type class for styling
+        statusMessage.className = `status-message ${type}`;
         statusMessage.textContent = message;
         statusMessage.style.display = 'block';