refactor: collapse single-implementation interfaces

Nine interfaces had exactly one implementation and no test double — they existed
only to be named twice in a DI registration: IFindingsStore, IFindingsStoreLocator,
IPrimeScheduleSignal, IRefineRunner, IWeekReportService, IMergeCoordinator,
IMissionControlPane, IOnlineLoginService, ITaskListFilter. Consumers now depend on
the concrete type; the DTO records that shared those files moved next to their
implementation. IInteractiveLaunchSpecService stays — it carries 54 lines of
contract documentation, which is not ceremony.

IMergeCoordinator in particular had a redundant null object: MergeCoordinator with
a null Handler already no-ops, and every test used the real class with Handler set.

Filtering/ collapses from 8 files to 1. ITaskListFilter and TaskListFilterBase were
a double abstraction over four predicates, with MatchesAsContext => false declared
in both. SmartFlagFilter also compiled its expression twice (its own _flag plus the
inherited Matches cache) — it now uses the cache.

StaticTokenAuthProvider was in src but production uses ZitadelAuthProvider; it is
a test double, so it moves to the test project. Its own test goes away with it.

src/ClaudeDo.Ui/ViewModels/MissionControlViewModel.cs

@@ -35,7 +35,7 @@ public sealed partial class MissionControlViewModel : ViewModelBase, IDisposable
 
     // Mirror of ConPtySessions typed as the pane abstraction so the layout toggle (grid/tabs)
     // binds one contract rather than a ConPTY-specific type.
-    public ObservableCollection<IMissionControlPane> Panes { get; } = new();
+    public ObservableCollection<ConPtyPaneViewModel> Panes { get; } = new();
 
     [ObservableProperty] private int _columnCount = 1;
 
@@ -43,7 +43,7 @@ public sealed partial class MissionControlViewModel : ViewModelBase, IDisposable
     [NotifyPropertyChangedFor(nameof(LayoutToggleLabel))]
     private bool _isFocusMode;
 
-    [ObservableProperty] private IMissionControlPane? _focusedPane;
+    [ObservableProperty] private ConPtyPaneViewModel? _focusedPane;
 
     public string LayoutToggleLabel => Loc.T(IsFocusMode ? "missionControl.overviewMode" : "missionControl.focusMode");
 
@@ -403,7 +403,7 @@ public sealed partial class MissionControlViewModel : ViewModelBase, IDisposable
             _    => 3,
         };
         OnPropertyChanged(nameof(HasPanes));
-        if (e.Action == NotifyCollectionChangedAction.Add && e.NewItems?[0] is IMissionControlPane added)
+        if (e.Action == NotifyCollectionChangedAction.Add && e.NewItems?[0] is ConPtyPaneViewModel added)
             FocusedPane = added;
         else if (e.Action == NotifyCollectionChangedAction.Remove && ReferenceEquals(FocusedPane, e.OldItems?[0]))
             FocusedPane = Panes.LastOrDefault();