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.Worker/Online/StaticTokenAuthProvider.cs

@@ -1,24 +0,0 @@
-using ClaudeDo.Worker.Online.Interfaces;
-
-namespace ClaudeDo.Worker.Online;
-
-/// <summary>
-/// Simple <see cref="IOnlineAuthProvider"/> that returns a fixed token supplied at construction.
-/// Used as the default DI registration until <c>ZitadelAuthProvider</c> is wired (Phase 2).
-/// Also serves as the test double.
-/// </summary>
-public sealed class StaticTokenAuthProvider : IOnlineAuthProvider
-{
-    private readonly string? _token;
-
-    public StaticTokenAuthProvider(string? token = null)
-    {
-        _token = token;
-    }
-
-    public Task<string?> GetAccessTokenAsync(CancellationToken ct = default)
-        => Task.FromResult(_token);
-
-    public Task<string?> GetAccessTokenAsync(bool forceRefresh, CancellationToken ct = default)
-        => Task.FromResult(_token);
-}