feat(proxy): flag managed-OAuth providers as routing-required

Managed-OAuth providers (github_copilot / codex_oauth / xai_oauth) need
proxy takeover to inject credentials, but the "needs routing" badge and
the switch-time warning only keyed off apiFormat — missing OAuth providers
whose upstream format is native (e.g. the new Codex xAI Grok OAuth preset
on openai_responses).

- Add isOAuthProviderType / OAUTH_PROVIDER_TYPES as the SSOT for OAuth types
- Extract providerNeedsRouting() as the authoritative predicate: managed
  OAuth always needs routing (the backend rejects these accounts' direct
  connection) regardless of apiFormat or Claude Desktop mode
- ProviderCard badges (claude / codex / claude-desktop) and the switch
  warning consume the shared predicate instead of raw apiFormat
- Gate the warning on per-app routing readiness: claude-desktop uses
  isProxyRunning (backend takeover status has no such field), other apps
  use isProxyTakeover — fixes false warnings on Desktop and missing
  warnings when the proxy runs but the app isn't taken over
- Force proxy mode for all managed-OAuth providers in the Claude Desktop
  form (lock the mode toggle), not only xai_oauth
- Add unit tests for providerNeedsRouting, the switch routing gate, and
  Desktop OAuth preset enforcement
- i18n(zh/en/ja/zh-TW): add notifications.proxyReasonManagedOAuth

src/config/constants.ts

@@ -5,6 +5,22 @@ export const PROVIDER_TYPES = {
   XAI_OAUTH: "xai_oauth",
 } as const;
 
+// 托管 OAuth 供应商类型：真实凭据由本地代理按请求注入，因此无论上游是否
+// 需要格式转换，都必须开启路由接管才能通过认证。新增此类预设时只需把
+// providerType 加进本数组，needsRouting 判定即自动覆盖，无需逐个特判。
+export const OAUTH_PROVIDER_TYPES: readonly string[] = [
+  PROVIDER_TYPES.GITHUB_COPILOT,
+  PROVIDER_TYPES.CODEX_OAUTH,
+  PROVIDER_TYPES.XAI_OAUTH,
+];
+
+/** 判断某 providerType 是否为托管 OAuth（凭据由代理注入、必须开启路由）。 */
+export function isOAuthProviderType(
+  providerType: string | null | undefined,
+): boolean {
+  return providerType != null && OAUTH_PROVIDER_TYPES.includes(providerType);
+}
+
 // 用量脚本模板类型常量
 export const TEMPLATE_TYPES = {
   CUSTOM: "custom",