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.Localization/locales/de.json

@@ -266,6 +266,7 @@
     "overviewMode": "Übersicht",
     "closeSession": "Sitzung schließen",
     "conptyLaunchFailed": "ConPTY-Sitzung konnte nicht geöffnet werden: {0}",
+    "planningTitleSuffix": " (Planung)",
     "question": {
       "title": "Claude fragt nach",
       "placeholder": "Antwort eingeben…",