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/MissionControl/ConPtyPaneViewModel.cs

@@ -11,7 +11,7 @@ namespace ClaudeDo.Ui.ViewModels.MissionControl;
 /// Claude session, or an ad-hoc/free session in a user-chosen directory (no task, <see cref="TaskId"/>
 /// is null — ad-hoc panes are never deduped, unlike task-based ones).
 /// </summary>
-public sealed partial class ConPtyPaneViewModel : ViewModelBase, IMissionControlPane, IDisposable
+public sealed partial class ConPtyPaneViewModel : ViewModelBase, IDisposable
 {
     public string? TaskId { get; }