style: add custom-scrollbar styling to all dialog scrollable areas

Added custom-scrollbar class to scrollable elements in:
- EffectBrowser dialog content area
- ProjectsDialog projects list
- CommandPalette results list
- Modal content area
- TrackList automation parameter label containers

This ensures consistent scrollbar styling across all dialogs and UI elements.

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

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

components/ui/Modal.tsx

@@ -102,7 +102,7 @@ export function Modal({
         </div>
 
         {/* Content */}
-        <div className="flex-1 overflow-y-auto p-4">
+        <div className="flex-1 overflow-y-auto custom-scrollbar p-4">
           {children}
         </div>