feat: MusicBrainz verification badge + MBID links in track details

Track details dialog now shows:

1. Green checkmark badge next to the track title when the recording
   has a MusicBrainz ID (hover: 'Metadata verified by MusicBrainz')

2. MusicBrainz section at the bottom with clickable MBID links for:
   - Recording (track) → musicbrainz.org/recording/{mbid}
   - Release Group (album) → musicbrainz.org/release-group/{mbid}
   - Artist → musicbrainz.org/artist/{mbid}

   Links open in the system browser. Only shown for entities that
   have MBIDs from audio file tags.

Backend: GetTrackMBIDs(filePath) Wails binding queries recording,
release_group, and artist mbid columns via a single JOIN query.
Frontend: loaded async when the dialog opens, non-blocking.

frontend/wailsjs/go/library/Library.d.ts

@@ -83,3 +83,11 @@ export function SetRescanHooks(arg1:library.RescanHooks):Promise<void>;
 export function SetScanHooks(arg1:library.ScanHooks):Promise<void>;
 
 export function SoftScanAllLibraries():Promise<void>;
+
+export interface TrackMBIDs {
+  recordingMbid: string;
+  releaseGroupMbid: string;
+  artistMbid: string;
+}
+
+export function GetTrackMBIDs(arg1:string):Promise<TrackMBIDs>;

frontend/wailsjs/go/library/Library.js

@@ -161,3 +161,7 @@ export function SetScanHooks(arg1) {
 export function SoftScanAllLibraries() {
   return window['go']['library']['Library']['SoftScanAllLibraries']();
 }
+
+export function GetTrackMBIDs(arg1) {
+  return window['go']['library']['Library']['GetTrackMBIDs'](arg1);
+}