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

hermes_cli/config.py

@@ -34,6 +34,7 @@ _EXTRA_ENV_KEYS = frozenset({
     "DISCORD_HOME_CHANNEL", "TELEGRAM_HOME_CHANNEL",
     "SIGNAL_ACCOUNT", "SIGNAL_HTTP_URL",
     "SIGNAL_ALLOWED_USERS", "SIGNAL_GROUP_ALLOWED_USERS",
+    "DINGTALK_CLIENT_ID", "DINGTALK_CLIENT_SECRET",
     "TERMINAL_ENV", "TERMINAL_SSH_KEY", "TERMINAL_SSH_PORT",
     "WHATSAPP_MODE", "WHATSAPP_ENABLED",
 })