feat: 实现 Builder API Key 系统级配置和 Gasless 交易支持

- 新增系统配置表（SystemConfig）用于存储 Builder API Key
- 实现 Builder API Key 的前端配置页面
- 集成 Builder Relayer API 支持 Gasless 交易
- 在 API 健康检查中添加 Builder Relayer API 检测
- 移除前端 API 测试功能，简化配置页面
- 修复赎回仓位时的 Builder API Key 检查逻辑
- 更新错误处理，引导用户配置 Builder API Key

frontend/src/locales/en/common.json

@@ -233,8 +233,10 @@
     "statistics": "Statistics",
     "users": "User Management",
     "systemSettings": "System",
+    "systemOverview": "Overview",
     "language": "Language",
     "apiHealth": "API Health",
+    "builderApiKey": "Builder API Key",
     "proxy": "Proxy",
     "notifications": "Notifications",
     "logout": "Logout",
@@ -302,6 +304,49 @@
     "systemSettingsDesc": "Configure proxy, view API health status",
     "footer": "Please use the above pages for configuration management."
   },
+  "builderApiKey": {
+    "title": "Builder API Key Configuration",
+    "alertTitle": "What is Builder API Key?",
+    "description": "Builder API Key is a system-level configuration, not related to your account. It is an API credential for Polymarket's Builder service, used to execute Gasless (no gas fee) transactions.",
+    "purposeTitle": "Main purposes:",
+    "purpose1": "Execute Gasless transactions: Operations like redeeming positions and creating orders don't require gas fees",
+    "purpose2": "Improve user experience: No need to prepare MATIC tokens in wallet for gas fees",
+    "purpose3": "Reduce transaction costs: Gas fees are covered by Builder service",
+    "getApiKey": "Get API Key:",
+    "openSettings": "Go to Polymarket Settings",
+    "apiKey": "Builder API Key",
+    "secret": "Builder Secret",
+    "passphrase": "Builder Passphrase",
+    "apiKeyPlaceholder": "Please enter Builder API Key",
+    "secretPlaceholder": "Please enter Builder Secret",
+    "passphrasePlaceholder": "Please enter Builder Passphrase",
+    "apiKeyHelp": "Configured, enter new value to update",
+    "secretHelp": "Configured, enter new value to update",
+    "passphraseHelp": "Configured, enter new value to update",
+    "saveSuccess": "Builder API Key configuration saved successfully",
+    "saveFailed": "Failed to save Builder API Key configuration",
+    "getFailed": "Failed to get Builder API Key configuration",
+    "notConfigured": "Builder API Key not configured, please go to System Settings to configure",
+    "notConfiguredError": "Builder API Key not configured, cannot execute Gasless transactions. Please go to System Settings to configure Builder API Key.",
+    "apiReference": "API Reference Documentation",
+    "apiReferenceDesc": "Learn more about Builder API usage:",
+    "relayerApiDocs": "Builder Relayer API Documentation",
+    "builderDocs": "Builder Development Documentation",
+    "apiTest": "API Test",
+    "apiTestDesc": "Test if Builder API is working correctly",
+    "testNonce": "Test Get Nonce",
+    "testNonceHelp": "Enter Safe address (proxyAddress)",
+    "testDeployed": "Test Check Deployed Status",
+    "testDeployedHelp": "Enter Safe address (proxyAddress)",
+    "testTransaction": "Test Get Transaction Status",
+    "testTransactionHelp": "Enter transaction ID",
+    "testAddressRequired": "Please enter address",
+    "testTransactionIdRequired": "Please enter transaction ID",
+    "testAddressPlaceholder": "Enter address, e.g., 0x...",
+    "testTransactionIdPlaceholder": "Enter transaction ID",
+    "testSuccess": "Test successful",
+    "testFailed": "Test failed"
+  },
   "resetPassword": {
     "title": "Reset Password",
     "firstUse": "First Time Using System",