Fix dropdown colours (vibe-kanban) (#891)

* Done! The dropdown colors are now fixed for dark mode readability:

- **Selected items** now use `bg-accent text-accent-foreground` instead of hardcoded light-theme colors
- **File paths** in selected items use `text-accent-foreground/70` for better contrast
- **Added accessibility** attributes (`aria-selected` and `role="option"`)

The changes maintain your existing design token pattern and will automatically adapt to both light and dark themes.

* Cleanup script changes for task attempt 9dd6bd96-f216-408c-ab42-94eefb1437e1

* Perfect! Now the selected dropdown item uses:

1. **Background:** `bg-primary/10` (subtle primary tint)
2. **Text:** `text-primary` (primary color text)
3. **Left border:** `border-l-2 border-primary` (visual indicator)
4. **File path:** `text-primary/70` (muted primary for secondary info)

This provides much better visual distinction while maintaining theme compatibility and using your existing design token pattern.

* Cleanup script changes for task attempt 9dd6bd96-f216-408c-ab42-94eefb1437e1

* Now the selected item uses `bg-muted text-foreground` which provides proper contrast in both light and dark modes, with a primary-colored left border for visual distinction. The file path uses consistent `text-muted-foreground` in all states.

* Cleanup script changes for task attempt 9dd6bd96-f216-408c-ab42-94eefb1437e1

* Perfect! Now the selected dropdown item simply uses `bg-muted text-foreground` which provides clear contrast and visibility without the border.

frontend/src/components/ui/file-search-textarea.tsx

@@ -287,13 +287,21 @@ export function FileSearchTextarea({
                     key={file.path}
                     className={`px-3 py-2 cursor-pointer text-sm ${
                       index === selectedIndex
-                        ? 'bg-blue-50 text-blue-900'
+                        ? 'bg-muted text-foreground'
                         : 'hover:bg-muted'
                     }`}
                     onClick={() => selectFile(file)}
+                    aria-selected={index === selectedIndex}
+                    role="option"
                   >
                     <div className="font-medium truncate">{file.name}</div>
-                    <div className="text-xs text-muted-foreground truncate">
+                    <div
+                      className={`text-xs truncate ${
+                        index === selectedIndex
+                          ? 'text-muted-foreground'
+                          : 'text-muted-foreground'
+                      }`}
+                    >
                       {file.path}
                     </div>
                   </div>