fix: clarify OpenAI OAuth proxy errors

frontend/src/i18n/locales/en.ts

@@ -2774,6 +2774,13 @@ export default {
             'Option 1: Copy the complete URL\n(http://localhost:xxx/auth/callback?code=...)\nOption 2: Copy only the code parameter value',
           authCodeHint:
             'You can copy the entire URL or just the code parameter value, the system will auto-detect',
+          failedToGenerateUrl: 'Failed to generate OpenAI auth URL',
+          failedToExchangeCode: 'Failed to exchange OpenAI auth code',
+          failedToValidateRT: 'Failed to validate refresh token',
+          errors: {
+            OPENAI_OAUTH_PROXY_REQUIRED:
+              'No proxy is configured and this server could not reach OpenAI directly, so the OpenAI OAuth request failed. Select a proxy that can access OpenAI and retry; if the authorization code has expired, regenerate the authorization URL.'
+          },
           // Refresh Token auth
           refreshTokenAuth: 'Manual RT Input',
           refreshTokenDesc: 'Enter your existing OpenAI Refresh Token(s). Supports batch input (one per line). The system will automatically validate and create accounts.',

frontend/src/i18n/locales/zh.ts

@@ -2911,6 +2911,13 @@ export default {
           authCodePlaceholder:
             '方式1：复制完整的链接\n(http://localhost:xxx/auth/callback?code=...)\n方式2：仅复制 code 参数的值',
           authCodeHint: '您可以直接复制整个链接或仅复制 code 参数值，系统会自动识别',
+          failedToGenerateUrl: '生成 OpenAI 授权链接失败',
+          failedToExchangeCode: 'OpenAI 授权码兑换失败',
+          failedToValidateRT: '验证 Refresh Token 失败',
+          errors: {
+            OPENAI_OAUTH_PROXY_REQUIRED:
+              '未设置代理，当前服务器无法直连 OpenAI，导致 OpenAI OAuth 请求失败。请先选择可访问 OpenAI 的代理后重试；如果授权码已失效，请重新生成授权链接。'
+          },
           // Refresh Token auth
           refreshTokenAuth: '手动输入 RT',
           refreshTokenDesc: '输入您已有的 OpenAI Refresh Token，支持批量输入（每行一个），系统将自动验证并创建账号。',