v1 task queue: add TASK 19-23 (transitions, hotkeys, media source, audio sync, studio mode)

- TASKS.md: added 5 new tasks for v1 feature completeness, execution order, updated backlog
- MONETIZATION.md: added v1 feature completeness section (competitive gap analysis)
- ai.md: added v1 task queue note in Current limitations/TODOs
- HANDOFF.md: updated session state and next steps
- ViewModels/SocialsDialogViewModel.cs: removed isPremium parameter (social slot locks)
- ViewModels/MainViewModel.cs: removed isPremium argument from SocialsDialogViewModel constructor
- ytLive.Tests/SocialsDialogViewModelTests.cs: updated 5 tests for unlocked slots

ViewModels/SocialsDialogViewModel.cs

@@ -204,7 +204,6 @@ public sealed class SocialsDialogViewModel : ViewModelBase
     private readonly ISocialValidator _validator;
     private readonly Func<Task<YouTubeChannel?>> _signInProvider;
     private readonly Func<Task> _signOutAction;
-    private readonly bool _isPremium;
     private readonly List<DialogEntry> _working = new();
     private readonly CancellationTokenSource _cts = new();
     private YouTubeChannel? _account;
@@ -218,13 +217,11 @@ public sealed class SocialsDialogViewModel : ViewModelBase
         Func<Task<YouTubeChannel?>> signInProvider,
         Func<Task> signOutAction,
         YouTubeChannel? account,
-        bool isPremium,
         SocialsConfig? current = null)
     {
         _validator = validator;
         _signInProvider = signInProvider;
         _signOutAction = signOutAction;
-        _isPremium = isPremium;
         _barEnabled = current?.BarEnabled ?? true;
         _account = account;
         _isSignedIn = account != null;
@@ -494,9 +491,9 @@ public sealed class SocialsDialogViewModel : ViewModelBase
                     slot.ProfileUrl = entry.ProfileUrl;
                     slot.FediverseSoftware = entry.FediverseSoftware;
                 }
-                else if (!_isPremium && i >= 2)
+                else if (i >= 2)
                 {
-                    slot.IsLocked = true;
+                    // Slot is empty — ready for user to add
                 }
             }
             slot.PropertyChanged += OnSlotPropertyChanged;