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/MergeCoordinator.cs

@@ -0,0 +1,21 @@
+using System;
+using System.Threading.Tasks;
+
+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.
+///
+/// DI singleton holding the resolver entry. The holder breaks the shell↔island construction
+/// cycle: islands depend on this type, the shell sets <see cref="Handler"/> after it is built.
+/// </summary>
+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; }
+
+    public Task ResolveConflictAsync(string taskId, string targetBranch) =>
+        Handler?.Invoke(taskId, targetBranch) ?? Task.CompletedTask;
+}