feat(S04/T01): Added DiscNumber field to MBTrack (populated from Medium…

- backend/explore/types.go
- backend/explore/musicbrainz.go
- frontend/wailsjs/go/explore/Service.d.ts
- frontend/index.ts

backend/explore/musicbrainz.go

@@ -388,10 +388,11 @@ func convertRelease(r musicbrainzws2.Release) MBRelease {
 	for _, m := range r.Media {
 		for _, t := range m.Tracks {
 			rel.Tracks = append(rel.Tracks, MBTrack{
-				Position: t.Position,
-				Title:    t.Title,
-				Length:   int(t.Length.Milliseconds()),
-				MBID:     string(t.ID),
+				Position:   t.Position,
+				DiscNumber: m.Position,
+				Title:      t.Title,
+				Length:     int(t.Length.Milliseconds()),
+				MBID:       string(t.ID),
 			})
 		}
 	}

backend/explore/types.go

@@ -59,10 +59,11 @@ type MBRecording struct {
 
 // MBTrack is a Wails-friendly projection of a MusicBrainz track.
 type MBTrack struct {
-	Position int    `json:"position"`
-	Title    string `json:"title"`
-	Length   int    `json:"length"`
-	MBID     string `json:"mbid"`
+	Position   int    `json:"position"`
+	DiscNumber int    `json:"discNumber"`
+	Title      string `json:"title"`
+	Length     int    `json:"length"`
+	MBID       string `json:"mbid"`
 }
 
 // LBTopRecording represents a popular recording from the