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

backend/internal/pkg/geminicli/oauth.go

@@ -181,19 +181,23 @@ func EffectiveOAuthConfig(cfg OAuthConfig, oauthType string) (OAuthConfig, error
 				effective.Scopes = DefaultAIStudioScopes
 			}
 		case "google_one":
-			// Google One accounts need generative-language scope for Gemini API access
-			// and drive.readonly scope for storage tier detection
-			effective.Scopes = DefaultGoogleOneScopes
+			// Google One uses built-in Gemini CLI client (same as code_assist)
+			// Built-in client can't request restricted scopes like generative-language.retriever
+			if isBuiltinClient {
+				effective.Scopes = DefaultCodeAssistScopes
+			} else {
+				effective.Scopes = DefaultGoogleOneScopes
+			}
 		default:
 			// Default to Code Assist scopes
 			effective.Scopes = DefaultCodeAssistScopes
 		}
-	} else if oauthType == "ai_studio" && isBuiltinClient {
+	} else if (oauthType == "ai_studio" || oauthType == "google_one") && isBuiltinClient {
 		// If user overrides scopes while still using the built-in client, strip restricted scopes.
 		parts := strings.Fields(effective.Scopes)
 		filtered := make([]string, 0, len(parts))
 		for _, s := range parts {
-			if strings.Contains(s, "generative-language") {
+			if hasRestrictedScope(s) {
 				continue
 			}
 			filtered = append(filtered, s)
@@ -219,6 +223,11 @@ func EffectiveOAuthConfig(cfg OAuthConfig, oauthType string) (OAuthConfig, error
 	return effective, nil
 }
 
+func hasRestrictedScope(scope string) bool {
+	return strings.HasPrefix(scope, "https://www.googleapis.com/auth/generative-language") ||
+		strings.HasPrefix(scope, "https://www.googleapis.com/auth/drive")
+}
+
 func BuildAuthorizationURL(cfg OAuthConfig, state, codeChallenge, redirectURI, projectID, oauthType string) (string, error) {
 	effectiveCfg, err := EffectiveOAuthConfig(cfg, oauthType)
 	if err != nil {