fix: resolve queued stream metadata in the background

Queue labels were only enriched through selected-entry playback. Resolve unplayed titles serially at utility priority, preempt enrichment for playback, and bind updates to queue item IDs.

Verified: make check-resolved check-queue check-youtube all.

Sources/App/PlaybackQueue.swift

@@ -5,6 +5,7 @@ struct PlaybackQueue {
         let id = UUID()
         let url: URL
         var label: String? = nil
+        var metadataAttempted = false
         var displayName: String { label ?? url.lastPathComponent }
     }
 
@@ -31,9 +32,10 @@ struct PlaybackQueue {
         items.append(contentsOf: entries.map { Item(url: $0.url, label: $0.label) })
     }
 
-    mutating func updateCurrentLabel(_ label: String) {
-        guard let index = currentIndex else { return }
-        items[index].label = label
+    mutating func updateLabel(_ label: String?, for id: UUID) {
+        guard let index = items.firstIndex(where: { $0.id == id }) else { return }
+        if let label { items[index].label = label }
+        items[index].metadataAttempted = true
     }
 
     mutating func append(_ urls: [URL]) {