refactor: drop the remaining single-implementation interfaces

IBaseDirtyChecker, IInteractiveLaunchSpecService and the LaunchSpec wrapper
had one implementation and one caller each; ProcessRunnerAdapter existed only
to give a static class an interface, and InstallArtifactLocator used
inheritance for two constructor arguments. The external MCP container now
shares its singletons through a Share<T> helper instead of 17 near-identical
registrations.

src/ClaudeDo.Worker/Git/BaseDirtyChecker.cs

@@ -13,12 +13,7 @@ public sealed record DirtyBaseWarning(int ModifiedCount, int UntrackedCount);
 /// files. Non-blocking by design: callers surface the counts as a heads-up, never refuse the
 /// transition.
 /// </summary>
-public interface IBaseDirtyChecker
-{
-    Task<DirtyBaseWarning?> CheckAsync(string? workingDir, CancellationToken ct);
-}
-
-public sealed class BaseDirtyChecker : IBaseDirtyChecker
+public sealed class BaseDirtyChecker
 {
     // Long enough to collapse every task in one batch_update_task_status call over the same
     // list into a single `git status` invocation; short enough that a later, independent queue