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.Ui/ViewModels/IslandsShellViewModel.cs

@@ -234,6 +234,11 @@ public sealed partial class IslandsShellViewModel : ViewModelBase, IDisposable
             OpenMissionControl();
             _ = MissionControl.OpenConPtySessionAsync(taskId);
         };
+        Tasks.OpenPlanningConPtyRequested += (taskId, resume) =>
+        {
+            OpenMissionControl();
+            _ = MissionControl.OpenPlanningConPtySessionAsync(taskId, resume);
+        };
         Tasks.TasksChanged     += (_, _) => _ = Lists.RefreshCountsAsync();
         Tasks.OpenListSettingsRequested += (_, _) =>
         {