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/Modals/MergeModalViewModel.cs

@@ -9,7 +9,7 @@ namespace ClaudeDo.Ui.ViewModels.Modals;
 public sealed partial class MergeModalViewModel : ViewModelBase
 {
     private readonly IWorkerClient _worker;
-    private readonly IMergeCoordinator _merge;
+    private readonly MergeCoordinator _merge;
 
     public string TaskId { get; set; } = "";
     public string TaskTitle { get; set; } = "";
@@ -42,7 +42,7 @@ public sealed partial class MergeModalViewModel : ViewModelBase
     /// True once a conflict has been handed off to the resolver — also a cue to close the diff window.
     public bool RoutedToResolver { get; private set; }
 
-    public MergeModalViewModel(IWorkerClient worker, IMergeCoordinator merge)
+    public MergeModalViewModel(IWorkerClient worker, MergeCoordinator merge)
     {
         _worker = worker;
         _merge = merge;