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.App/Program.cs

@@ -128,7 +128,6 @@ sealed class Program
 
         // Conflict-merge coordinator: single seam the shell wires to its resolver entry.
         sc.AddSingleton<MergeCoordinator>();
-        sc.AddSingleton<IMergeCoordinator>(sp => sp.GetRequiredService<MergeCoordinator>());
 
         // ViewModels
         sc.AddTransient<DiffViewerViewModel>();
@@ -139,7 +138,7 @@ sealed class Program
         sc.AddTransient<MergeHelperSelectionModalViewModel>();
         sc.AddSingleton<IPrimeScheduleApi, WorkerPrimeScheduleApi>();
         sc.AddSingleton<INotesApi, WorkerNotesApi>();
-        sc.AddSingleton<IOnlineLoginService, OnlineLoginService>();
+        sc.AddSingleton<OnlineLoginService>();
         sc.AddTransient<PrimeClaudeTabViewModel>();
         sc.AddTransient<SettingsModalViewModel>();
         sc.AddTransient<MergeModalViewModel>();
@@ -173,7 +172,7 @@ sealed class Program
                 sp.GetRequiredService<IWorkerClient>(),
                 sp,
                 sp.GetRequiredService<INotesApi>(),
-                sp.GetRequiredService<IMergeCoordinator>()));
+                sp.GetRequiredService<MergeCoordinator>()));
         sc.AddSingleton<UsagePillViewModel>(sp =>
             new UsagePillViewModel(sp.GetRequiredService<IWorkerClient>()));
         sc.AddSingleton<MissionControlViewModel>(sp =>