fix: improve App Config slide-in panel layout

- Narrowed panel from 640px to 520px so main table columns stay visible
- Settings grid uses CSS grid (3 columns) for proper wrapping
- Removed unused PanelActions component that caused white footer bar

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/pages/Admin/AppConfigPage.tsx

@@ -284,22 +284,9 @@ export default function AppConfigPage() {
         onClose={() => setSelectedApp(null)}
         title={selectedApp ?? ''}
         className={styles.widePanel}
-        actions={selectedApp ? <PanelActions appId={selectedApp} onClose={() => setSelectedApp(null)} /> : undefined}
       >
         {selectedApp && <AppConfigDetail appId={selectedApp} onClose={() => setSelectedApp(null)} />}
       </DetailPanel>
     </div>
   );
 }
-
-function PanelActions({ appId, onClose }: { appId: string; onClose: () => void }) {
-  // Edit/Save/Cancel actions rendered in the panel footer
-  const { data: config } = useApplicationConfig(appId);
-  const updateConfig = useUpdateApplicationConfig();
-  const { toast } = useToast();
-  const [editing, setEditing] = useState(false);
-
-  // This is a simplified stub — the actual editing state is managed inside AppConfigDetail.
-  // For now, the actions slot is reserved for future use.
-  return null;
-}