feat(gateway): add DingTalk platform adapter (#1685)

Add DingTalk as a messaging platform using the dingtalk-stream SDK
for real-time message reception via Stream Mode (no webhook needed).
Replies are sent via session webhook using markdown format.

Features:
- Stream Mode connection (long-lived WebSocket, no public URL needed)
- Text and rich text message support
- DM and group chat support
- Message deduplication with 5-minute window
- Auto-reconnection with exponential backoff
- Session webhook caching for reply routing

Configuration:
  export DINGTALK_CLIENT_ID=your-app-key
  export DINGTALK_CLIENT_SECRET=your-app-secret

  # or in config.yaml:
  platforms:
    dingtalk:
      enabled: true
      extra:
        client_id: your-app-key
        client_secret: your-app-secret

Files:
- gateway/platforms/dingtalk.py (340 lines) — adapter implementation
- gateway/config.py — add DINGTALK to Platform enum
- gateway/run.py — add DingTalk to _create_adapter
- hermes_cli/config.py — add env vars to _EXTRA_ENV_KEYS
- hermes_cli/tools_config.py — add dingtalk to PLATFORMS
- tests/gateway/test_dingtalk.py — 21 tests

gateway/run.py

@@ -1132,6 +1132,13 @@ class GatewayRunner:
                 return None
             return EmailAdapter(config)
 
+        elif platform == Platform.DINGTALK:
+            from gateway.platforms.dingtalk import DingTalkAdapter, check_dingtalk_requirements
+            if not check_dingtalk_requirements():
+                logger.warning("DingTalk: dingtalk-stream not installed or DINGTALK_CLIENT_ID/SECRET not set")
+                return None
+            return DingTalkAdapter(config)
+
         return None
     
     def _is_user_authorized(self, source: SessionSource) -> bool: