Make voice note loading completely lazy with deferred initialization

Aggressive performance optimization to prevent UI freezes:

Problem: Even with async loading, creating 10+ VoiceNotePlaybackController
instances simultaneously (when scrolling past multiple voice notes) spawned
20+ concurrent background tasks, potentially starving main thread.

Solution - Ultra-lazy loading:
1. VoiceNotePlaybackController.init() now does ZERO work
   - No duration loading
   - No player creation
   - Instant initialization

2. Duration loaded on-demand via public loadDuration() method
   - Called from VoiceNoteView.onAppear after 150ms delay
   - Reduced priority: .utility instead of .userInitiated
   - Guard prevents duplicate loading

3. Waveform loading also deferred 150ms
   - Gives UI time to settle after message appears
   - Prevents task storms when multiple voice notes appear

This spreads the work over time instead of all at once.

bitchat/Features/voice/VoiceNotePlaybackController.swift

@@ -16,12 +16,14 @@ final class VoiceNotePlaybackController: NSObject, ObservableObject, AVAudioPlay
     init(url: URL) {
         self.url = url
         super.init()
-        // Load duration asynchronously to avoid blocking main thread
-        loadDurationAsync()
+        // Don't load anything eagerly - wait until user interaction or view is fully displayed
     }
 
-    private func loadDurationAsync() {
-        DispatchQueue.global(qos: .userInitiated).async { [weak self] in
+    func loadDuration() {
+        // Only load if not already loaded
+        guard duration == 0 else { return }
+
+        DispatchQueue.global(qos: .utility).async { [weak self] in
             guard let self = self else { return }
             do {
                 let player = try AVAudioPlayer(contentsOf: self.url)
@@ -44,7 +46,8 @@ final class VoiceNotePlaybackController: NSObject, ObservableObject, AVAudioPlay
         stop()
         self.url = url
         player = nil
-        loadDurationAsync()
+        duration = 0
+        // Duration will be loaded on demand when needed
     }
 
     func togglePlayback() {

bitchat/Views/Media/VoiceNoteView.swift

@@ -100,10 +100,13 @@ struct VoiceNoteView: View {
                 .stroke(borderColor, lineWidth: 1)
         )
         .onAppear {
-            WaveformCache.shared.waveform(for: url, completion: { bins in
-                self.waveform = bins
-            })
-            // No need to call playback.replaceURL - already initialized with correct URL
+            // Defer both duration and waveform loading to let UI settle after message appears
+            DispatchQueue.main.asyncAfter(deadline: .now() + 0.15) {
+                playback.loadDuration()
+                WaveformCache.shared.waveform(for: url, completion: { bins in
+                    self.waveform = bins
+                })
+            }
         }
         .onChange(of: url) { newValue in
             WaveformCache.shared.waveform(for: newValue, completion: { bins in