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.

tests/ClaudeDo.Worker.Tests/Planning/WindowsTerminalLauncherTests.cs

@@ -70,6 +70,31 @@ public sealed class WindowsTerminalLauncherTests
         Assert.DoesNotContain("CLAUDEDO_LAUNCH_PROMPT", command);
     }
 
+    [Fact]
+    public void BuildPlanningStartArgs_HasPlanningFlagsAndKickoffLast()
+    {
+        var ctx = MakeStartCtx();
+
+        var args = WindowsTerminalLauncher.BuildPlanningStartArgs(ctx);
+
+        Assert.Equal("--model", args[0]);
+        var permIdx = args.ToList().IndexOf("--permission-mode");
+        Assert.True(permIdx >= 0);
+        Assert.Equal("plan", args[permIdx + 1]);
+        Assert.Contains("--allowedTools", args);
+        Assert.Contains(ctx.Files.SessionDirectory, args);
+        Assert.Contains(ctx.Files.SystemPromptPath, args);
+        // Kickoff positional is the last token and points at the brief file.
+        Assert.Contains(ctx.Files.InitialPromptPath, args[^1]);
+    }
+
+    [Fact]
+    public void BuildPlanningResumeArgs_PinsPlanModeAndResume()
+    {
+        var args = WindowsTerminalLauncher.BuildPlanningResumeArgs("sess-9");
+        Assert.Equal(new[] { "--permission-mode", "plan", "--resume", "sess-9" }, args);
+    }
+
     [Fact]
     public void BuildResumeCommand_ResumesSessionSingleQuoted()
     {