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/Findings/FindingsStore.cs

@@ -4,13 +4,29 @@ using ClaudeDo.Worker.Git;
 
 namespace ClaudeDo.Worker.Findings;
 
+/// <summary>One durable finding, as handed in by a caller. Git and DB lookups happen above this layer.</summary>
+public sealed record FindingInput(
+    string Slug,
+    string Title,
+    string Body,
+    string Scope,
+    string SourceTaskId,
+    string VerifiedAgainst);
+
+public sealed record SaveFindingOutcome(
+    string Slug,
+    string Path,
+    bool Created,
+    int TotalFindings,
+    bool NearCapacity);
+
 /// <summary>
 /// Owns &lt;working-dir&gt;/.claudedo/ — one markdown file per finding plus a rebuilt INDEX.md.
 /// Pure filesystem: the caller supplies the head commit and source task id.
 /// INDEX.md is always regenerated from the files on disk, never patched, so findings the user
 /// deleted or renamed by hand disappear from the index on the next write.
 /// </summary>
-public sealed class FindingsStore : IFindingsStore
+public sealed class FindingsStore
 {
     /// <summary>INDEX.md is read by every run; past this many entries it stops paying for itself.</summary>
     public const int WarnThreshold = 80;

src/ClaudeDo.Worker/Findings/FindingsStoreLocator.cs

@@ -3,12 +3,15 @@ using ClaudeDo.Data.Repositories;
 
 namespace ClaudeDo.Worker.Findings;
 
+/// <summary>The main checkout a finding belongs to, plus whether its store is committed with the repo.</summary>
+public sealed record FindingsTarget(string ListId, string ListName, string WorkingDir, bool Tracked);
+
 /// <summary>
 /// Maps an MCP call to the project whose findings store it targets. Always resolves to the list's
 /// WorkingDir — the main checkout — even when the caller runs inside a worktree, because concurrent
 /// writes into worktree copies would produce INDEX.md merge conflicts.
 /// </summary>
-public sealed class FindingsStoreLocator : IFindingsStoreLocator
+public sealed class FindingsStoreLocator
 {
     private readonly TaskRepository _tasks;
     private readonly ListRepository _lists;

src/ClaudeDo.Worker/Findings/Interfaces/IFindingsStore.cs

@@ -1,22 +0,0 @@
-namespace ClaudeDo.Worker.Findings;
-
-/// <summary>One durable finding, as handed in by a caller. Git and DB lookups happen above this layer.</summary>
-public sealed record FindingInput(
-    string Slug,
-    string Title,
-    string Body,
-    string Scope,
-    string SourceTaskId,
-    string VerifiedAgainst);
-
-public sealed record SaveFindingOutcome(
-    string Slug,
-    string Path,
-    bool Created,
-    int TotalFindings,
-    bool NearCapacity);
-
-public interface IFindingsStore
-{
-    Task<SaveFindingOutcome> SaveAsync(string workingDir, FindingInput input, CancellationToken ct, bool tracked = false);
-}

src/ClaudeDo.Worker/Findings/Interfaces/IFindingsStoreLocator.cs

@@ -1,10 +0,0 @@
-namespace ClaudeDo.Worker.Findings;
-
-/// <summary>The main checkout a finding belongs to, plus whether its store is committed with the repo.</summary>
-public sealed record FindingsTarget(string ListId, string ListName, string WorkingDir, bool Tracked);
-
-public interface IFindingsStoreLocator
-{
-    Task<FindingsTarget> ResolveForTaskAsync(string taskId, CancellationToken ct);
-    Task<FindingsTarget> ResolveForListAsync(string listIdOrName, CancellationToken ct);
-}