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.

tests/ClaudeDo.Worker.Tests/Infrastructure/TaskStateServiceBuilder.cs

@@ -24,7 +24,7 @@ public static class TaskStateServiceBuilder
     public static Built Build(
         IDbContextFactory<ClaudeDoDbContext> dbFactory,
         Func<IActiveMergeState>? mergeState = null,
-        IBaseDirtyChecker? baseDirtyChecker = null)
+        BaseDirtyChecker? baseDirtyChecker = null)
     {
         var hub = new CapturingHubContext();
         var broadcaster = new HubBroadcaster(hub);