fix(gateway): fail-closed external-surface defaults + profile-aware multiplex authz

Aligns runtime behaviour with SECURITY.md 2.6: externally reachable
messaging adapters must fail closed unless access is explicitly
configured. Closes the confirmed multiplex authorization bypass a
secondary profile's open dm/group policy no longer inherits the default
profile's allowlist trust.

- Own-policy adapters (WhatsApp, WeCom, Weixin, QQBot, Yuanbao) default
  dm_policy/group_policy to pairing/allowlist instead of open; open now
  requires an explicit GATEWAY_ALLOW_ALL_USERS or per-platform allow-all.
- Startup guard (_own_policy_open_startup_violation) refuses to boot when
  an enabled adapter is open without the allow-all opt-in; the guard now
  runs for every secondary profile in multiplex mode too.
- Profile-aware own-policy authorization: _authorization_adapter /
  _adapter_for_source resolve the live adapter via SessionSource.profile,
  so _is_user_authorized and the ingress/pairing/busy/queue paths read the
  originating profile's adapter policy, not the default profile's.
- Fail-closed intake for Email, Feishu P2P, and Discord (blank-principal
  denial, empty-allowlist deny, missing-interaction.user deny).

Salvaged from #44073 (external-surface hardening), split into a focused
gateway-authz PR per maintainer request. Follow-up fix by Hermes Agent:
the Discord slash-auth channel bypass now matches DISCORD_ALLOWED_CHANNELS
by the same name-inclusive keys (id + name + #name + parent) the on_message
scope gate uses, so a name-form channel allowlist authorizes slash
interactions consistently (was id-only, breaking #name matching).

Co-authored-by: Hermes Agent <agent@nousresearch.com>

plugins/platforms/feishu/adapter.py

@@ -4200,6 +4200,17 @@ class FeishuAdapter(BasePlatformAdapter):
                 return "bot_not_mentioned"
 
         if not is_group:
+            if os.getenv("FEISHU_ALLOW_ALL_USERS", "").strip().lower() in {"true", "1", "yes"}:
+                return None
+            if os.getenv("GATEWAY_ALLOW_ALL_USERS", "").strip().lower() in {"true", "1", "yes"}:
+                return None
+            # Empty FEISHU_ALLOWED_USERS is the pairing-mode default from setup:
+            # forward DMs to gateway intake so the pairing handshake can run.
+            # Gateway auth fail-closes agent access until approval.
+            if not self._allowed_group_users:
+                return None
+            if not (sender_ids and (sender_ids & self._allowed_group_users)):
+                return "dm_policy_rejected"
             return None
 
         if not self._allow_group_message(