fix(worker): keep interactive & planning prompts intact past Windows Terminal

wt.exe treats ';' as a command/tab delimiter in every argument, with no escape
that survives quoting (microsoft/terminal#13264), so a task description
containing ';' spawned extra terminals on "Run interactively" and planning start.
Route the launch as wt -> powershell -> claude and pass the free-text prompt via
$env:CLAUDEDO_LAUNCH_PROMPT so it never reaches the wt command line; PowerShell
binds the variable as a single argument (embedded quotes escaped for PS 5.1).

Also clarify the launcher, which serves interactive runs too (not just planning):
IPlanningTerminalLauncher -> ITerminalLauncher, WindowsTerminalPlanningLauncher ->
WindowsTerminalLauncher, LaunchStart/Resume -> LaunchPlanning{Start,Resume}Async.

src/ClaudeDo.Worker/Planning/Interfaces/ITerminalLauncher.cs

@@ -0,0 +1,16 @@
+namespace ClaudeDo.Worker.Planning;
+
+// Launches the Claude CLI in a visible terminal for human-driven sessions:
+// planning (start/resume) and the ad-hoc "Run interactively" action. Not used for
+// headless task execution (that path is ClaudeProcess, prompt over stdin).
+public interface ITerminalLauncher
+{
+    Task LaunchPlanningStartAsync(PlanningSessionStartContext ctx, CancellationToken cancellationToken);
+    Task LaunchPlanningResumeAsync(PlanningSessionResumeContext ctx, CancellationToken cancellationToken);
+    Task LaunchInteractiveAsync(InteractiveLaunchContext ctx, CancellationToken cancellationToken);
+}
+
+public sealed class TerminalLaunchException : Exception
+{
+    public TerminalLaunchException(string message) : base(message) { }
+}