refactor(gemini): 简化用量窗口显示为等级+限流状态

- 前端：移除进度条和限额文本，只显示 tier badge + 限流状态/倒计时
- 后端：token provider 自动保存 tier_id 到账号凭证
- 优化：tier 名称简化为 Free/Pro/Ultra
- 显示格式：[Free] 未限流 / [Pro] 限流 2m 35s

backend/internal/service/gemini_token_provider.go

@@ -118,6 +118,7 @@ func (p *GeminiTokenProvider) GetAccessToken(ctx context.Context, account *Accou
 			return accessToken, nil
 		}
 		detected = strings.TrimSpace(detected)
+		tierID = strings.TrimSpace(tierID)
 		if detected != "" {
 			if account.Credentials == nil {
 				account.Credentials = make(map[string]any)