feat(planning): run interactive planning sessions via embedded ConPTY

Planning start/resume opened an external Windows Terminal (wt) window.
Route them through the embedded ConPTY Command Center pane instead, matching
the existing interactive-session UX (no external window).

- Extract bare planning arg builders (BuildPlanningStartArgs/ResumeArgs) from
  WindowsTerminalLauncher; the wt path still uses them (kept, not removed).
- InteractiveLaunchSpecService.BuildPlanningStart/Resume map a planning
  context into a LaunchSpec (planning args + env: MAX_THINKING_TOKENS,
  CLAUDEDO_PLANNING_TOKEN). Hub GetPlanningStart/ResumeLaunchSpec run
  StartAsync/ResumeAsync then return the spec.
- UI: OpenPlanningSession + the resume branch raise OpenPlanningConPtyRequested;
  the shell opens Mission Control and hosts a planning ConPTY pane.

Env is process-global by design (sequential human-paced sessions). wt planning
code retained. Tests added for the arg/env mapping.

src/ClaudeDo.Worker/Hub/WorkerHub.cs

@@ -673,6 +673,38 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
         return _interactiveLaunchSpec.BuildForDirectoryAsync(directory, Context.ConnectionAborted);
     });
 
+    // Starts a planning session (worktree + prompt files + token, task -> Planning) and returns
+    // the launch spec for an embedded ConPTY planning terminal -- the ConPTY replacement for
+    // StartPlanningSessionAsync's external wt window. On any spec-build failure the just-started
+    // session is discarded (no children exist yet), mirroring StartPlanningSessionAsync.
+    public Task<LaunchSpec> GetPlanningStartLaunchSpec(string taskId) => HubGuard(async () =>
+    {
+        if (_interactiveLaunchSpec is null)
+            throw new InvalidOperationException("Interactive launch spec service is not configured.");
+        var ctx = await _planning.StartAsync(taskId, Context.ConnectionAborted);
+        try
+        {
+            var spec = _interactiveLaunchSpec.BuildPlanningStart(ctx);
+            await Clients.All.SendAsync("TaskUpdated", taskId);
+            return spec;
+        }
+        catch
+        {
+            await _planning.DiscardAsync(taskId, dequeueQueuedChildren: true, Context.ConnectionAborted);
+            throw;
+        }
+    });
+
+    // Resumes a planning session and returns the ConPTY launch spec (--permission-mode plan
+    // --resume). ConPTY replacement for ResumePlanningSessionAsync's external wt window.
+    public Task<LaunchSpec> GetPlanningResumeLaunchSpec(string taskId) => HubGuard(async () =>
+    {
+        if (_interactiveLaunchSpec is null)
+            throw new InvalidOperationException("Interactive launch spec service is not configured.");
+        var ctx = await _planning.ResumeAsync(taskId, Context.ConnectionAborted);
+        return _interactiveLaunchSpec.BuildPlanningResume(ctx);
+    });
+
     public async Task<DiscardPlanningOutcome> DiscardPlanningSessionAsync(string taskId, bool dequeueQueuedChildren = false)
     {
         var outcome = await _planning.DiscardAsync(taskId, dequeueQueuedChildren, Context.ConnectionAborted);