feat(gateway): add WeCom callback-mode adapter for self-built apps

Add a second WeCom integration mode for regular enterprise self-built
applications.  Unlike the existing bot/websocket adapter (wecom.py),
this handles WeCom's standard callback flow: WeCom POSTs encrypted XML
to an HTTP endpoint, the adapter decrypts, queues for the agent, and
immediately acknowledges.  The agent's reply is delivered proactively
via the message/send API.

Key design choice: always acknowledge immediately and use proactive
send — agent sessions take 3-30 minutes, so the 5-second inline reply
window is never useful.  The original PR's Future/pending-reply
machinery was removed in favour of this simpler architecture.

Features:
- AES-CBC encrypt/decrypt (BizMsgCrypt-compatible)
- Multi-app routing scoped by corp_id:user_id
- Legacy bare user_id fallback for backward compat
- Access-token management with auto-refresh
- WECOM_CALLBACK_* env var overrides
- Port-in-use pre-check before binding
- Health endpoint at /health

Salvaged from PR #7774 by @chqchshj.  Simplified by removing the
inline reply Future system and fixing: secrets.choice for nonce
generation, immediate plain-text acknowledgment (not encrypted XML
containing 'success'), and initial token refresh error handling.

tools/cronjob_tools.py

@@ -456,7 +456,7 @@ Important safety rule: cron-run sessions should not recursively schedule more cr
             },
             "deliver": {
                 "type": "string",
-                "description": "Delivery target: origin, local, telegram, discord, slack, whatsapp, signal, weixin, matrix, mattermost, homeassistant, dingtalk, feishu, wecom, email, sms, bluebubbles, or platform:chat_id or platform:chat_id:thread_id for Telegram topics. Examples: 'origin', 'local', 'telegram', 'telegram:-1001234567890:17585', 'discord:#engineering'"
+                "description": "Delivery target: origin, local, telegram, discord, slack, whatsapp, signal, weixin, matrix, mattermost, homeassistant, dingtalk, feishu, wecom, wecom_callback, email, sms, bluebubbles, or platform:chat_id or platform:chat_id:thread_id for Telegram topics. Examples: 'origin', 'local', 'telegram', 'telegram:-1001234567890:17585', 'discord:#engineering'"
             },
             "skills": {
                 "type": "array",

tools/send_message_tool.py

@@ -158,6 +158,7 @@ def _handle_send(args):
         "dingtalk": Platform.DINGTALK,
         "feishu": Platform.FEISHU,
         "wecom": Platform.WECOM,
+        "wecom_callback": Platform.WECOM_CALLBACK,
         "weixin": Platform.WEIXIN,
         "email": Platform.EMAIL,
         "sms": Platform.SMS,