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);
-}

src/ClaudeDo.Ui/Services/MergeCoordinator.cs

@@ -6,20 +6,12 @@ namespace ClaudeDo.Ui.Services;
 /// <summary>
 /// Single entry point for handing a conflicting merge to the in-app 3-pane resolver.
 /// Replaces the per-VM <c>RequestConflictResolution</c> Func seams that used to be
-/// hand-threaded shell → details → merge-section → diff → merge-modal. The shell wires
-/// <see cref="MergeCoordinator.Handler"/> once at composition; invokers depend only on
-/// this interface (injected via DI).
-/// </summary>
-public interface IMergeCoordinator
-{
-    Task ResolveConflictAsync(string taskId, string targetBranch);
-}
-
-/// <summary>
+/// hand-threaded shell → details → merge-section → diff → merge-modal.
+///
 /// DI singleton holding the resolver entry. The holder breaks the shell↔island construction
-/// cycle: islands depend on the interface, the shell sets <see cref="Handler"/> after it is built.
+/// cycle: islands depend on this type, the shell sets <see cref="Handler"/> after it is built.
 /// </summary>
-public sealed class MergeCoordinator : IMergeCoordinator
+public sealed class MergeCoordinator
 {
     /// Set once at composition to the shell's resolver entry. Null (headless/tests) ⇒ no-op.
     public Func<string, string, Task>? Handler { get; set; }

src/ClaudeDo.Ui/Services/OnlineLoginService.cs

@@ -6,7 +6,9 @@ using Duende.IdentityModel.OidcClient.Browser;
 
 namespace ClaudeDo.Ui.Services;
 
-public sealed class OnlineLoginService : IOnlineLoginService
+public sealed record OnlineLoginResult(bool Success, string? RefreshToken, string? Error, string? Warning = null);
+
+public sealed class OnlineLoginService
 {
     public async Task<OnlineLoginResult> LoginAsync(
         string authority, string clientId, string scope, string redirectUri,