chore(servers): remove quick/full scan buttons from server cards (#843)

Drops the Quick/Full scan actions and all supporting logic — they are no
longer needed. Removes the ServerScanActions component (incl. the unused
compact variant), the subsonicScan API, the scanStore, and the app-root
useScanPolling hook (no more background scan polling). Cleans up the
.server-scan-* CSS and the settings.scan i18n block across all 9 locales.

440 deletions, no new code; tsc + bundle clean.

src/app/MainApp.tsx

@@ -14,7 +14,6 @@ import { useGlobalShortcutsStore } from '../store/globalShortcutsStore';
 import { initHotCachePrefetch } from '../hotCachePrefetch';
 import { initMiniPlayerBridgeOnMain } from '../utils/miniPlayerBridge';
 import { runAdvancedModeMigration } from '../utils/migrations/advancedModeMigration';
-import { useScanPolling } from '../hooks/useScanPolling';
 import { IS_WINDOWS } from '../utils/platform';
 import TauriEventBridge from './TauriEventBridge';
 import AppShell from './AppShell';
@@ -35,8 +34,6 @@ export default function MainApp() {
   // Advanced Mode toggle. Idempotent — flagged in localStorage.
   useEffect(() => { runAdvancedModeMigration(); }, []);
 
-  useScanPolling();
-
   // Push playback state to mini window + handle control events.
   useEffect(() => {
     return initMiniPlayerBridgeOnMain();