feat(interactive): fresh-worktree-on-demand + ad-hoc launch specs

BuildForTaskAsync now creates a worktree on demand (via WorktreeManager.CreateAsync,
the same path TaskRunner uses) when a task has a configured working dir but no
Active/Kept worktree, returning a fresh-start spec -- so never-run tasks can be
opened interactively. Adds BuildForDirectoryAsync + GetAdHocLaunchSpec hub/client
for ad-hoc sessions in an arbitrary directory (no task, no worktree, no skill seeding).

src/ClaudeDo.Worker/Hub/WorkerHub.cs

@@ -671,6 +671,15 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
         return _interactiveLaunchSpec.BuildForTaskAsync(taskId, Context.ConnectionAborted);
     });
 
+    // Builds the launch spec for an ad-hoc interactive session in an arbitrary directory --
+    // no task, no worktree, no session-skills seeding.
+    public Task<LaunchSpec> GetAdHocLaunchSpec(string directory) => HubGuard(() =>
+    {
+        if (_interactiveLaunchSpec is null)
+            throw new InvalidOperationException("Interactive launch spec service is not configured.");
+        return _interactiveLaunchSpec.BuildForDirectoryAsync(directory, Context.ConnectionAborted);
+    });
+
     public Task SendInteractiveMessage(string taskId, string text) =>
         _interactive.SendAsync(taskId, text, Context.ConnectionAborted);