feat(worker): in-app interactive session service, replacing the wt terminal launch

InteractiveSessionService resolves a task's list working dir + seeded prompt,
spawns a StreamingClaudeSession (claude stream-json in the list dir, model+auto
as before), registers it in LiveSessionRegistry, streams output over TaskMessage,
and broadcasts InteractiveSessionStarted/Ended (an exit watcher fires Ended). The
hub's OpenInteractiveTerminalAsync now starts this in-app session; SendInteractiveMessage
and StopInteractiveSession route to it. The external Windows-Terminal interactive
launch (LaunchInteractiveAsync / InteractiveLaunchContext / OpenInteractiveAsync) is
removed; planning sessions keep their terminal launch.

src/ClaudeDo.Worker/Hub/HubBroadcaster.cs

@@ -77,4 +77,10 @@ public sealed class HubBroadcaster : IPrimeBroadcaster, IRefineBroadcaster
     Task IRefineBroadcaster.RefineStartedAsync(string taskId) => RefineStarted(taskId);
     Task IRefineBroadcaster.RefineFinishedAsync(string taskId, bool success, string? error) =>
         RefineFinished(taskId, success, error);
+
+    public Task InteractiveSessionStarted(string taskId) =>
+        _hub.Clients.All.SendAsync("InteractiveSessionStarted", taskId);
+
+    public Task InteractiveSessionEnded(string taskId) =>
+        _hub.Clients.All.SendAsync("InteractiveSessionEnded", taskId);
 }