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/nl/settings.ts

@@ -468,16 +468,4 @@ export const settings = {
   floatingPlayerBarSub: 'Houd de spelerbalk zwevend boven de inhoud',
   uiScaleTitle: 'Interface schaal',
   uiScaleLabel: 'Zoom',
-  scan: {
-    quick: 'Snel scannen',
-    full: 'Volledige scan',
-    quickTip: 'Snel scannen — nieuwe/gewijzigde bestanden indexeren',
-    fullTip: 'Volledige scan — alles opnieuw indexeren',
-    confirmFull: 'Klik nogmaals om te bevestigen',
-    confirmFullShort: 'Volledige scan bevestigen',
-    scanning: 'Scannen…',
-    done: 'Scan voltooid',
-    error: 'Scan mislukt',
-    toast: '{{name}}: scan voltooid — {{count}} tracks geïndexeerd',
-  },
 };