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/Planning/Interfaces/ITerminalLauncher.cs

@@ -2,7 +2,7 @@ namespace ClaudeDo.Worker.Planning;
 
 // Launches the Claude CLI in a visible terminal for human-driven planning sessions.
 // Not used for headless task execution (that path is ClaudeProcess, prompt over stdin)
-// nor for embedded ConPTY interactive sessions (those use IInteractiveLaunchSpecService).
+// nor for embedded ConPTY interactive sessions (those use InteractiveLaunchSpecService).
 public interface ITerminalLauncher
 {
     Task LaunchPlanningStartAsync(PlanningSessionStartContext ctx, CancellationToken cancellationToken);