test: 更新客户端 IP 设置响应契约

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/internal/server/api_contract_test.go

@@ -791,6 +791,7 @@ func TestAPIContracts(t *testing.T) {
 						"site_subtitle": "Subtitle",
 						"api_base_url": "https://api.example.com",
 						"api_key_acl_trust_forwarded_ip": false,
+					"forwarded_client_ip_headers": [],
 					"contact_info": "support",
 					"doc_url": "https://docs.example.com",
 					"auth_source_default_email_balance": 0,
@@ -1102,6 +1103,7 @@ func TestAPIContracts(t *testing.T) {
 					"site_subtitle": "Subscription to API Conversion Platform",
 					"api_base_url": "",
 					"api_key_acl_trust_forwarded_ip": false,
+					"forwarded_client_ip_headers": [],
 					"contact_info": "",
 					"doc_url": "",
 					"home_content": "",