feat(system): add restart server endpoint with authentication

docs/api.md

@@ -129,6 +129,32 @@ X-Timestamp: 1704067200000
 
 ---
 
+## Restart Server
+
+**Endpoint:** `/system/restart`
+**Method:** GET
+**Permission Level:** Admin
+
+**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:**
+```json
+{
+  "success": true,
+  "message": "Restarting server..."
+}
+```
+
+---
+
 ## Register User
 
 **Endpoint:** `/register`