feat(09-03): add scan control UI with pause/resume/cancel and confirmation dialog

- Pause/Resume buttons replace Soft Scan/Full Rescan during active scan
- Cancel button shows confirmation dialog with Keep/Discard/Continue options
- Register LibraryScanPaused/Resumed/Cancelled event handlers
- Status bar shows 'Scan paused.' with accent color when paused
- Add CancelScan/PauseScan/ResumeScan Wails binding stubs
- Cancel dialog overlay dismissible by clicking outside or Continue Scanning
- Add cancelled field to ScanMetrics TypeScript interface

frontend/wailsjs/go/library/Library.js

@@ -2,6 +2,10 @@
 // Cynhyrchwyd y ffeil hon yn awtomatig. PEIDIWCH Â MODIWL
 // This file is automatically generated. DO NOT EDIT
 
+export function CancelScan() {
+  return window['go']['library']['Library']['CancelScan']();
+}
+
 export function FullRescan() {
   return window['go']['library']['Library']['FullRescan']();
 }
@@ -10,6 +14,14 @@ export function GetAlbumTracks(arg1) {
   return window['go']['library']['Library']['GetAlbumTracks'](arg1);
 }
 
+export function IsScanActive() {
+  return window['go']['library']['Library']['IsScanActive']();
+}
+
+export function IsScanPaused() {
+  return window['go']['library']['Library']['IsScanPaused']();
+}
+
 export function GetAlbumsByArtist(arg1) {
   return window['go']['library']['Library']['GetAlbumsByArtist'](arg1);
 }
@@ -34,6 +46,14 @@ export function GetTracksByGenre(arg1) {
   return window['go']['library']['Library']['GetTracksByGenre'](arg1);
 }
 
+export function PauseScan() {
+  return window['go']['library']['Library']['PauseScan']();
+}
+
+export function ResumeScan() {
+  return window['go']['library']['Library']['ResumeScan']();
+}
+
 export function Scan() {
   return window['go']['library']['Library']['Scan']();
 }