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

tests/components/ClaudeDesktopProviderForm.test.tsx

@@ -30,6 +30,35 @@ function renderForm(
 }
 
 describe("ClaudeDesktopProviderForm", () => {
+  it.each(["github_copilot", "codex_oauth", "xai_oauth"])(
+    "托管 OAuth %s 即使旧数据是 direct 也强制开启模型映射",
+    (providerType) => {
+      renderForm({
+        name: "Managed OAuth Provider",
+        category: "third_party",
+        settingsConfig: {
+          env: {
+            ANTHROPIC_BASE_URL: "https://api.example.com",
+          },
+        },
+        meta: {
+          providerType,
+          claudeDesktopMode: "direct",
+          apiFormat: "anthropic",
+          claudeDesktopModelRoutes: {
+            "claude-sonnet-5": { model: "upstream-model" },
+          },
+        },
+      });
+
+      const modelMappingToggle = screen.getByRole("switch", {
+        name: "需要模型映射",
+      });
+      expect(modelMappingToggle).toBeChecked();
+      expect(modelMappingToggle).toBeDisabled();
+    },
+  );
+
   it("编辑模型映射的菜单显示名时保持输入框焦点", () => {
     renderForm({
       name: "Proxy Provider",