fix(gateway): gate profile routing on multiplex_profiles + widen batch-key routing to all adapters

Follow-ups on the salvaged #20096 profile-routing feature:

- _profile_name_for_source now returns None unless gateway.multiplex_profiles
  is on. Routing stamps source.profile, which namespaces session/batch keys,
  but the profile-scoped agent run only activates under multiplexing — without
  the gate, configured routes with multiplexing off split batch/session keys
  into agent:<profile> while the agent still ran from agent:main.
- Widen the profile-aware _text_batch_key fix from Discord to every adapter
  that builds batch keys via build_session_key (telegram, whatsapp, matrix,
  feishu, wecom, weixin) — routing is platform-generic, so the batch-key
  namespace fix must be too.
- Downgrade the no-route-matched log from INFO to DEBUG (fired on every
  unrouted inbound message).
- GatewayConfig.to_dict(): serialize profile_routes as plain dicts
  (ProfileRoute dataclasses are not JSON-safe).
- Docs: correct the 'independent of multiplexing' claim in
  docs/profile-routing.md (routing requires multiplexing), fix the
  platform-only specificity row (0, not 1), and document profile_routes in
  website/docs/user-guide/multi-profile-gateways.md.
- Tests: pin the multiplex gate (routes ignored when off, active when on,
  build_source end-to-end stays in agent:main when off).

plugins/platforms/feishu/adapter.py

@@ -3633,6 +3633,7 @@ class FeishuAdapter(BasePlatformAdapter):
             event.source,
             group_sessions_per_user=self.config.extra.get("group_sessions_per_user", True),
             thread_sessions_per_user=self.config.extra.get("thread_sessions_per_user", False),
+            profile=event.source.profile,
         )
 
     @staticmethod