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/locales/de/settings.ts

@@ -470,16 +470,4 @@ export const settings = {
   floatingPlayerBarSub: 'Player-Leiste über dem Inhalt schweben lassen',
   uiScaleTitle: 'Interface-Skalierung',
   uiScaleLabel: 'Zoom',
-  scan: {
-    quick: 'Quick-Scan',
-    full: 'Full-Scan',
-    quickTip: 'Quick-Scan — nur neue/geänderte Dateien indexieren',
-    fullTip: 'Full-Scan — alles neu indexieren',
-    confirmFull: 'Nochmal klicken zum Bestätigen',
-    confirmFullShort: 'Full-Scan bestätigen',
-    scanning: 'Scannt…',
-    done: 'Scan fertig',
-    error: 'Scan fehlgeschlagen',
-    toast: '{{name}}: Scan fertig — {{count}} Tracks indexiert',
-  },
 };