fix: Ensure consistent main content padding when debug panel is closed

Add minimum bottom padding (48px) when the debug panel is closed to
prevent Kanban cards from being cut off at the bottom of the viewport.

ui/src/App.tsx

@@ -331,7 +331,7 @@ function App() {
       {/* Main Content */}
       <main
         className="max-w-7xl mx-auto px-4 py-8"
-        style={{ paddingBottom: debugOpen ? debugPanelHeight + 32 : undefined }}
+        style={{ paddingBottom: debugOpen ? debugPanelHeight + 32 : 48 }}
       >
         {!selectedProject ? (
           <div className="text-center mt-12">