feat(gemini): 优化 OAuth 和配额展示

主要改进：
- 修复 google_one OAuth scopes 配置问题
- 添加 Gemini 账号配额展示组件
- 优化 Code Assist 类型检测逻辑
- 添加 OAuth 测试用例

frontend/src/composables/useGeminiOAuth.ts

@@ -12,6 +12,8 @@ export interface GeminiTokenInfo {
   expires_at?: number | string
   project_id?: string
   oauth_type?: string
+  tier_id?: string
+  extra?: Record<string, unknown>
   [key: string]: unknown
 }
 
@@ -122,10 +124,16 @@ export function useGeminiOAuth() {
       expires_at: expiresAt,
       scope: tokenInfo.scope,
       project_id: tokenInfo.project_id,
-      oauth_type: tokenInfo.oauth_type
+      oauth_type: tokenInfo.oauth_type,
+      tier_id: tokenInfo.tier_id
     }
   }
 
+  const buildExtraInfo = (tokenInfo: GeminiTokenInfo): Record<string, unknown> | undefined => {
+    if (!tokenInfo.extra || typeof tokenInfo.extra !== 'object') return undefined
+    return tokenInfo.extra
+  }
+
   const getCapabilities = async (): Promise<GeminiOAuthCapabilities | null> => {
     try {
       return await adminAPI.gemini.getCapabilities()
@@ -145,6 +153,7 @@ export function useGeminiOAuth() {
     generateAuthUrl,
     exchangeAuthCode,
     buildCredentials,
+    buildExtraInfo,
     getCapabilities
   }
 }