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- Security: force token_uri to Google default, preventing SSRF via crafted service account JSON
- Dedup: extract shared getVertexServiceAccountAccessToken() to eliminate ~35 lines of duplication between ClaudeTokenProvider and GeminiTokenProvider
- Fix: apply model mapping + Vertex model ID normalization in forward_as_responses and forward_as_chat_completions paths
- Fix: exclude service_account from AI Studio endpoint selection (Vertex cannot serve generativelanguage.googleapis.com)
- Feature: add model restriction/mapping UI for service_account in EditAccountModal
- Dedup: extract VERTEX_LOCATION_OPTIONS to shared constants
- i18n: replace all hardcoded Chinese strings in Vertex UI with translation keys

Introduce OAuthRefreshAPI as the single entry point for all OAuth token
refresh operations, eliminating the race condition where background
refresh and inline refresh could simultaneously use the same
refresh_token (fixes #1035).

Key changes:
- Add OAuthRefreshExecutor interface extending TokenRefresher with CacheKey
- Add OAuthRefreshAPI.RefreshIfNeeded with lock → DB re-read → double-check flow
- Add ProviderRefreshPolicy / BackgroundRefreshPolicy strategy types
- Simplify all 4 TokenProviders to delegate to OAuthRefreshAPI
- Rewrite TokenRefreshService.refreshWithRetry to use unified API path
- Add MergeCredentials and BuildClaudeAccountCredentials helpers
- Add 40 unit tests covering all new and modified code paths

上次修复(2665230a)只阻止了写入缓存，但仍返回旧token导致403。
现在版本过时时直接使用DB中的最新token返回。

- 重构 IsTokenVersionStale 为 CheckTokenVersion，返回最新account
- 消除重复DB查询，复用版本检查时已获取的account

- 新增 _token_version 版本号机制，防止过期 token 污染缓存
- TokenRefreshService 刷新成功后写入版本号并清除缓存
- TokenProvider 写入缓存前检查版本，过时则跳过
- ClearError 时同步清除 token 缓存

- Gemini 缓存键统一增加 gemini: 前缀，避免与其他平台命名空间冲突
- OAuth 账号 401 错误时设置 expires_at=now 并持久化，强制下次请求刷新 token
- Redis 锁获取失败时降级为无锁刷新，仅在 token 接近过期时执行，并检查 ctx 取消状态
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

新增 OpenAI/Claude TokenProvider 与缓存键生成
扩展 OAuth 缓存失效覆盖更多平台
统一 OAuth 缓存前缀与依赖注入