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/SettingsModalViewModel.cs

@@ -73,7 +73,7 @@ public sealed partial class SettingsModalViewModel : ViewModelBase
     public Action? CloseAction { get; set; }
 
     public SettingsModalViewModel(IWorkerClient worker, PrimeClaudeTabViewModel prime,
-                                  IOnlineLoginService onlineLoginService,
+                                  OnlineLoginService onlineLoginService,
                                   ILocalizer localizer, AppSettings appSettings,
                                   IDbContextFactory<ClaudeDoDbContext> dbFactory)
     {