fix(13-02): resolve phantom playlist tracks using M3U8 paths after scan

- Add ScanHooks callback struct to library package (follows RemovalHooks pattern)
- Move phantom resolution from library to playlist service via hook
- New ResolvePhantomTracksAfterScan reads M3U8 files and resolves paths
  against current audio_files using multi-root resolution
- Handles pre-existing phantoms (match by M3U8 position) and new ones
  (match by phantom_file_path)
- Delete old resolvePhantomTracks method that required phantom_file_path
- Wire ScanHooks in app.go OnStartup

frontend/wailsjs/go/playlist/Service.js

@@ -86,6 +86,10 @@ export function ResolvePhantomTracks(arg1, arg2) {
   return window['go']['playlist']['Service']['ResolvePhantomTracks'](arg1, arg2);
 }
 
+export function ResolvePhantomTracksAfterScan() {
+  return window['go']['playlist']['Service']['ResolvePhantomTracksAfterScan']();
+}
+
 export function RestoreAllPlaylists() {
   return window['go']['playlist']['Service']['RestoreAllPlaylists']();
 }