Support server health check by http://localhost:<port>/v1/system/healthz (#10150)

### What problem does this PR solve?

Support server health check. Solved issue: #10106

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

docs/references/http_api_reference.md

@@ -4102,3 +4102,77 @@ Failure:
 ```
 
 ---
+
+### System
+---
+### Check system health
+
+**GET** `/v1/system/healthz`
+
+Check the health status of RAGFlow’s dependencies (database, Redis, document engine, object storage).
+
+#### Request
+
+- Method: GET
+- URL: `/v1/system/healthz`
+- Headers:
+  - 'Content-Type: application/json'
+  (no Authorization required)
+
+##### Request example
+
+```bash
+curl --request GET
+     --url http://{address}/v1/system/healthz
+     --header 'Content-Type: application/json'
+```
+
+##### Request parameters
+
+- `address`: (*Path parameter*), string  
+  The host and port of the backend service (e.g., `localhost:7897`).
+
+---
+
+#### Responses
+
+- **200 OK** – All services healthy
+
+```http
+HTTP/1.1 200 OK
+Content-Type: application/json
+
+{
+  "db": "ok",
+  "redis": "ok",
+  "doc_engine": "ok",
+  "storage": "ok",
+  "status": "ok"
+}
+```
+
+- **500 Internal Server Error** – At least one service unhealthy
+
+```http
+HTTP/1.1 500 INTERNAL SERVER ERROR
+Content-Type: application/json
+
+{
+  "db": "ok",
+  "redis": "nok",
+  "doc_engine": "ok",
+  "storage": "ok",
+  "status": "nok",
+  "_meta": {
+    "redis": {
+      "elapsed": "5.2",
+      "error": "Lost connection!"
+    }
+  }
+}
+```
+
+Explanation:  
+- Each service is reported as "ok" or "nok".  
+- The top-level `status` reflects overall health.  
+- If any service is "nok", detailed error info appears in `_meta`.