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/Services/Interfaces/IOnlineLoginService.cs

@@ -1,10 +0,0 @@
-namespace ClaudeDo.Ui.Services;
-
-public sealed record OnlineLoginResult(bool Success, string? RefreshToken, string? Error, string? Warning = null);
-
-public interface IOnlineLoginService
-{
-    Task<OnlineLoginResult> LoginAsync(
-        string authority, string clientId, string scope, string redirectUri,
-        CancellationToken ct = default);
-}