feat(channel-service): add Python FastAPI pywechat channel service

- Add FastAPI project under channel-service/
- Implement mock pywechat client adapter (login, send, heartbeat)
- Add /v1/wechat-personal/login/*, /v1/wechat-personal/send/* APIs
- Add /v1/heartbeat and /v1/monitor/status for client health
- Add /monitor HTML page with Web Components
- Add pytest suite and Dockerfile
- Update .gitignore for Python/Node artifacts

channel-service/app/services/heartbeat_service.py

@@ -0,0 +1,32 @@
+from __future__ import annotations
+
+import time
+
+from app.clients.pywechat_client import ClientRegistry, OnlineStatus, registry
+
+
+class HeartbeatService:
+    def __init__(self, registry: ClientRegistry):
+        self.registry = registry
+
+    def heartbeat(self, account_id: str, payload: dict) -> dict:
+        client = self.registry.get_or_create(account_id, payload.get("account_name"))
+        client.heartbeat()
+        if "risk_level" in payload:
+            client.state.risk_level = payload["risk_level"]
+        if "sent_count_today" in payload:
+            client.state.sent_count_today = payload["sent_count_today"]
+        return {"success": True, "account_id": account_id}
+
+    def check_offline_accounts(self, timeout_seconds: int = 120) -> list[dict]:
+        now = time.time()
+        offline = []
+        for client in self.registry.list_all():
+            last = client.state.last_heartbeat_at
+            if client.state.online_status == OnlineStatus.ONLINE and (last is None or now - last > timeout_seconds):
+                client.state.online_status = OnlineStatus.OFFLINE
+                offline.append({"account_id": client.state.account_id, "last_heartbeat_at": last})
+        return offline
+
+
+heartbeat_service = HeartbeatService(registry)