feat: add StepFun and Nous Portal provider support (#140)

- Add StepFun provider (API key auth, STEPFUN_API_KEY)
- Add Nous Portal provider with full OAuth device code flow
  (device code request → poll for token → mint agent key → save to auth.json)
- Add NousLoginModal component for OAuth UI (user code display + verification link)
- Update ProviderFormModal to handle Nous OAuth flow (hide API key fields)
- Add nous-auth backend controller and routes
- Update PROVIDER_ENV_MAP with stepfun and nous entries
- Add i18n translations for Nous OAuth in all 8 locales

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

packages/client/src/i18n/locales/zh.ts

@@ -268,6 +268,13 @@ export default {
     codexOpenLink: '打开授权页面',
     codexApproved: '登录成功',
     codexExpired: '授权已过期，请重试。',
+    nousLoginTitle: 'Nous Portal 登录',
+    nousWaiting: '在授权页面输入此代码完成登录:',
+    nousCopyCode: '代码已复制',
+    nousOpenLink: '打开授权页面',
+    nousApproved: '登录成功',
+    nousDenied: '授权被拒绝，请重试。',
+    nousExpired: '授权已过期，请重试。',
     noProviders: '暂无 Provider，添加一个开始吧。',
     builtIn: '内置',
     customType: '自定义',