feat(openai): 支持自动透传开关并透传 User-Agent

- OpenAI OAuth/API Key 统一支持自动透传开关，编辑页可开关\n- 透传模式仅替换认证并保留计费/并发/审计，修复 API Key responses 端点拼接\n- Usage 页面显示原始 User-Agent 且不截断，补充回归测试与清单

frontend/src/i18n/locales/en.ts

@@ -1533,7 +1533,8 @@ export default {
         apiKeyHint: 'Your OpenAI API Key',
         oauthPassthrough: 'Auto passthrough (auth only)',
         oauthPassthroughDesc:
-          'When enabled, applies to Codex CLI requests only: the gateway forwards request/response as-is and only swaps OAuth auth, while keeping billing/concurrency/audit. Disable to rollback if you hit 4xx or compatibility issues.',
+          'When enabled, this OpenAI account uses automatic passthrough: the gateway forwards request/response as-is and only swaps auth, while keeping billing/concurrency/audit and necessary safety filtering.',
+        modelRestrictionDisabledByPassthrough: 'Automatic passthrough is enabled: model whitelist/mapping will not take effect.',
         enableSora: 'Enable Sora simultaneously',
         enableSoraHint: 'Sora uses the same OpenAI account. Enable to create Sora account simultaneously.'
       },

frontend/src/i18n/locales/zh.ts

@@ -1682,7 +1682,8 @@ export default {
         apiKeyHint: '您的 OpenAI API Key',
         oauthPassthrough: '自动透传（仅替换认证）',
         oauthPassthroughDesc:
-          '开启后，仅对 Codex CLI 请求生效：网关将原样透传请求与响应内容，只替换 OAuth 认证并保留计费/并发/审计；如遇 4xx/兼容性问题可关闭回滚。',
+          '开启后，该 OpenAI 账号将自动透传请求与响应，仅替换认证并保留计费/并发/审计及必要安全过滤；如遇兼容性问题可随时关闭回滚。',
+        modelRestrictionDisabledByPassthrough: '已开启自动透传：模型白名单/映射不会生效。',
         enableSora: '同时启用 Sora',
         enableSoraHint: 'Sora 使用相同的 OpenAI 账号，开启后将同时创建 Sora 平台账号'
       },