fix: add 6s timeout to MusicService Supabase fetch for offline fallback

When airplane mode is active, the Supabase client hung indefinitely
waiting for a network response, blocking the mock track fallback.
Now races the query against a 6-second Task.sleep so mock tracks
load immediately after timeout.

tabatago-swift/TabataGo/Services/MusicService.swift

@@ -50,9 +50,6 @@ actor MusicService {
     // ─── Supabase Fetch ──────────────────────────────────────────
 
     private func fetchFromSupabase(vibe: MusicVibe) async -> [MusicTrack]? {
-        // Re-use the existing SupabaseService's client configuration.
-        // We build our own client here because SupabaseService is an actor
-        // and doesn't expose the raw client.
         guard !AppEnvironment.isPreview else { return nil }
 
         let urlRaw = Bundle.main.infoDictionary?["SUPABASE_URL"] as? String ?? ""
@@ -63,16 +60,30 @@ actor MusicService {
         }
 
         let client = SupabaseClient(supabaseURL: url, supabaseKey: key)
+        let genres = vibe.genres
 
         do {
-            let rows: [DownloadItemRow] = try await client
-                .from("download_items")
-                .select("id, video_id, title, duration_seconds, public_url, storage_path, genre")
-                .eq("status", value: "completed")
-                .in("genre", values: vibe.genres)
-                .limit(50)
-                .execute()
-                .value
+            let rows: [DownloadItemRow] = try await withThrowingTaskGroup(of: [DownloadItemRow].self) { group in
+                group.addTask {
+                    try await client
+                        .from("download_items")
+                        .select("id, video_id, title, duration_seconds, public_url, storage_path, genre")
+                        .eq("status", value: "completed")
+                        .in("genre", values: genres)
+                        .limit(50)
+                        .execute()
+                        .value
+                }
+                group.addTask {
+                    try await Task.sleep(for: .seconds(6))
+                    throw CancellationError()
+                }
+                guard let result = try await group.next() else {
+                    return []
+                }
+                group.cancelAll()
+                return result
+            }
 
             let tracks: [MusicTrack] = rows.compactMap { row in
                 guard let trackURL = row.resolvedURL(supabaseBase: urlRaw) else { return nil }