feat(sys): add self-check functionality for system settings and frpc binary

docs/api.md

@@ -20,6 +20,7 @@ All API responses are returned in JSON format:
 ```
 
 **Important Notes:**
+- All endpoints are relative to the base URL `/api`
 - For all requests: Authentication token and timestamp are sent in HTTP headers (prefixed with `X-`)
 - For **POST** requests: Other data is sent in the request body as JSON
 - For **GET** requests: All data is sent in HTTP headers (prefixed with `X-`)
@@ -90,6 +91,44 @@ Get software version and build information.
 
 ---
 
+## Self Check
+
+**Endpoint:** `/system/selfCheck`  
+**Method:** POST  
+**Content-Type:** application/json
+**Permission Level:** Visitor
+
+Check the system configuration and frpc binary.
+
+**Request Headers:**
+```
+X-Token: your_token
+X-Timestamp: 1704067200000
+```
+| Header | Type | Required | Description |
+|--------|------|----------|-------------|
+| X-Token | string | Yes | Authentication token |
+| X-Timestamp | int64 | Yes | Client timestamp in milliseconds |
+
+**Response (Success):**
+```json
+{
+  "success": true,
+  "message": "Self check passed"
+}
+```
+> If there were any errors, the response will be in error format.
+
+**Response (Error):**
+```json
+{
+  "success": false,
+  "message": "error message"
+}
+```
+
+---
+
 ## Register User
 
 **Endpoint:** `/register`