fix(docs): update stale docstring to reflect shipped inbound delivery paths

The module docstring claimed "No inbound A2A server is bundled here yet"
but A2AServer (push) and PollDelivery (poll) have been implemented and
documented since Phase 30.8b/30.8c. Replaced the outdated claim with a
concise description of both delivery modes and how run_agent_loop uses them.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

molecule_agent/client.py

@@ -11,10 +11,19 @@ a Phase 30 endpoint:
 * :py:meth:`run_heartbeat_loop` — drives heartbeat + state-poll on a timer,
   returns when the platform reports the workspace paused or deleted.
 
-No inbound A2A server is bundled here yet — that requires hosting an HTTP
-endpoint the platform's proxy can reach, which is network-dependent.
-Use :class:`molecule_agent.a2a_server.A2AServer` to add inbound A2A support.
-See that module for usage and the Phase 30.8b contract.
+The client also exposes two inbound delivery paths for handling platform-initiated
+A2A messages:
+
+* **Push mode** — :class:`molecule_agent.a2a_server.A2AServer` hosts an HTTP server
+  in a background thread; platform pushes inbound A2A as HTTP requests. Use when the
+  agent has a publicly reachable URL (cloud VM, ngrok tunnel, etc.).
+* **Poll mode** — :class:`molecule_agent.inbound.PollDelivery` polls
+  ``GET /workspaces/:id/activity`` on a configurable interval; no public URL required.
+  The default when no explicit delivery is passed to :py:meth:`run_agent_loop`.
+
+Both feed the same :py:class:`molecule_agent.inbound.MessageHandler` callback.
+Reply routing (``/notify`` for canvas users, ``/a2a`` for peer agents) is handled
+automatically by :py:meth:`reply`.
 """
 from __future__ import annotations