feat(worker): WindowsTerminalPlanningLauncher with pre-flight checks

src/ClaudeDo.Worker/Planning/IPlanningTerminalLauncher.cs

@@ -0,0 +1,12 @@
+namespace ClaudeDo.Worker.Planning;
+
+public interface IPlanningTerminalLauncher
+{
+    Task LaunchStartAsync(PlanningSessionStartContext ctx, CancellationToken cancellationToken);
+    Task LaunchResumeAsync(PlanningSessionResumeContext ctx, CancellationToken cancellationToken);
+}
+
+public sealed class PlanningLaunchException : Exception
+{
+    public PlanningLaunchException(string message) : base(message) { }
+}