fix(ws2): register @app.command(/new-task) so Slack slash command is acked

'the app did not respond': serve() registered @app.action/@app.event but NO
@app.command handler, so Bolt never acked the /new-task slash command within
Slack's ~3s deadline. Add an @app.command(/new-task) handler that ack()s first,
re-stamps type:slash_commands onto Bolt's inner command body (Bolt strips the
Socket Mode envelope type that _is_new_task_command/_discriminating_type expect),
then forwards to handle_event (AUTHZ-01 + new-task dispatch). The resulting
payload shape is the one already covered by test_new_task_calls_callback_*.

agent-team/agent_team/transport/slack_listener.py

@@ -523,6 +523,21 @@ class SlackListener:
         def _on_mention(body: Mapping[str, Any]) -> None:
             _forward(body)
 
+        # Slash commands (e.g. /new-task) MUST be ack()'d within ~3s or Slack
+        # shows "the app did not respond". Bolt delivers the INNER command
+        # payload (command / text / user_id / channel_id) WITHOUT the Socket
+        # Mode envelope's ``type``, so re-stamp ``type: "slash_commands"`` to
+        # match what handle_event's _is_new_task_command + _discriminating_type
+        # expect, then forward (handle_event runs AUTHZ-01 + the new-task
+        # dispatch). Ack FIRST so the 3s deadline is met even though start_task
+        # then runs the clarifier to the first gate synchronously.
+        @app.command(_NEW_TASK_COMMAND)
+        def _on_command(ack: Any, body: Mapping[str, Any]) -> None:
+            ack()
+            payload = dict(body)
+            payload.setdefault("type", "slash_commands")
+            _forward(payload)
+
         handler = SocketModeHandler(app, self._app_token)
         self._socket_handler = handler
         handler.start()