feat(dingtalk): proactive messaging via Robot OpenAPI + send_message_tool media

- Add DingTalk access-token management (_dingtalk_fetch_access_token,
  _dingtalk_fetch_oapi_token) with process-wide cache, 5 min safety
  margin, and asyncio.Lock for concurrent safety.
- Add _dingtalk_upload_media() — upload local files to /media/upload
  (legacy OAPI token) with mime auto-detection and 20 MB guard.
- Add _dingtalk_classify_chat_id() — route on chat_id shape:
  'cidXXX==' → group /groupMessages/send, plain staffId or
  'user:<staffId>' → 1:1 /oToMessages/batchSend.
- Add dingtalk_send_proactive() orchestrator — text + media delivery.
- In send(), fall back to dingtalk_send_proactive() when no session
  webhook is cached (proactive/cron/cross-platform delivery).
- Fix /sethome DM chat_id: persist 'user:<staffId>' instead of DM
  conversation_id so proactive DM delivery works (gateway/run.py).
- Enhance send_message_tool.py: MEDIA:<path> tag extraction, native
  DingTalk/Feishu routing with media_files support.
- Update test assertions for proactive-send error path.

pyproject.toml

@@ -76,7 +76,15 @@ termux = [
   "hermes-agent[honcho]",
   "hermes-agent[acp]",
 ]
-dingtalk = ["dingtalk-stream>=0.20,<1", "alibabacloud-dingtalk>=2.0.0", "qrcode>=7.0,<8"]
+dingtalk = [
+  "dingtalk-stream>=0.20,<1",
+  "alibabacloud-dingtalk>=2.0.0",
+  "qrcode>=7.0,<8",
+  # File content parsing for rich-media messages (docx/pdf/xlsx)
+  "python-docx>=1.0,<2",
+  "pdfplumber>=0.10,<1",
+  "openpyxl>=3.1,<4",
+]
 feishu = ["lark-oapi>=1.5.3,<2", "qrcode>=7.0,<8"]
 web = ["fastapi>=0.104.0,<1", "uvicorn[standard]>=0.24.0,<1"]
 rl = [