feat(gemini): 添加 Google One 存储空间推断 Tier 功能

## 功能概述
通过 Google Drive API 获取存储空间配额来推断 Google One 订阅等级，并优化统一的配额显示系统。

## 后端改动
- 新增 Drive API 客户端 (drive_client.go)
  - 支持代理和指数退避重试
  - 处理 403/429 错误
- 添加 Tier 推断逻辑 (inferGoogleOneTier)
  - 支持 6 种 tier 类型：AI_PREMIUM, GOOGLE_ONE_STANDARD, GOOGLE_ONE_BASIC, FREE, GOOGLE_ONE_UNKNOWN, GOOGLE_ONE_UNLIMITED
- 集成到 OAuth 流程
  - ExchangeCode: 授权时自动获取 tier
  - RefreshAccountToken: Token 刷新时更新 tier (24小时缓存)
- 新增管理 API 端点
  - POST /api/v1/admin/accounts/:id/refresh-tier (单个账号刷新)
  - POST /api/v1/admin/accounts/batch-refresh-tier (批量刷新)

## 前端改动
- 更新 AccountQuotaInfo.vue
  - 添加 Google One tier 标签映射
  - 添加 tier 颜色样式 (紫色/蓝色/绿色/灰色/琥珀色)
- 更新 AccountUsageCell.vue
  - 添加 Google One tier 显示逻辑
  - 根据 oauth_type 区分显示方式
- 添加国际化翻译 (en.ts, zh.ts)
  - aiPremium, standard, basic, free, personal, unlimited

## Tier 推断规则
- >= 2TB: AI Premium
- >= 200GB: Google One Standard
- >= 100GB: Google One Basic
- >= 15GB: Free
- > 100TB: Unlimited (G Suite legacy)
- 其他/失败: Unknown (显示为 Personal)

## 优雅降级
- Drive API 失败时使用 GOOGLE_ONE_UNKNOWN
- 不阻断 OAuth 流程
- 24小时缓存避免频繁调用

## 测试
- ✅ 后端编译成功
- ✅ 前端构建成功
- ✅ 所有代码符合现有规范

backend/internal/pkg/geminicli/drive_client.go

@@ -0,0 +1,113 @@
+package geminicli
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"time"
+
+	"github.com/Wei-Shaw/sub2api/internal/pkg/httpclient"
+)
+
+// DriveStorageInfo represents Google Drive storage quota information
+type DriveStorageInfo struct {
+	Limit int64 `json:"limit"` // Storage limit in bytes
+	Usage int64 `json:"usage"` // Current usage in bytes
+}
+
+// DriveClient interface for Google Drive API operations
+type DriveClient interface {
+	GetStorageQuota(ctx context.Context, accessToken, proxyURL string) (*DriveStorageInfo, error)
+}
+
+type driveClient struct {
+	httpClient *http.Client
+}
+
+// NewDriveClient creates a new Drive API client
+func NewDriveClient() DriveClient {
+	return &driveClient{
+		httpClient: &http.Client{
+			Timeout: 10 * time.Second,
+		},
+	}
+}
+
+// GetStorageQuota fetches storage quota from Google Drive API
+func (c *driveClient) GetStorageQuota(ctx context.Context, accessToken, proxyURL string) (*DriveStorageInfo, error) {
+	const driveAPIURL = "https://www.googleapis.com/drive/v3/about?fields=storageQuota"
+
+	req, err := http.NewRequestWithContext(ctx, "GET", driveAPIURL, nil)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create request: %w", err)
+	}
+
+	req.Header.Set("Authorization", "Bearer "+accessToken)
+
+	// Get HTTP client with proxy support
+	client, err := httpclient.GetClient(httpclient.Options{
+		ProxyURL: proxyURL,
+		Timeout:  10 * time.Second,
+	})
+	if err != nil {
+		return nil, fmt.Errorf("failed to create HTTP client: %w", err)
+	}
+
+	// Retry logic with exponential backoff for rate limits
+	var resp *http.Response
+	maxRetries := 3
+	for attempt := 0; attempt < maxRetries; attempt++ {
+		resp, err = client.Do(req)
+		if err != nil {
+			return nil, fmt.Errorf("failed to execute request: %w", err)
+		}
+
+		// Success
+		if resp.StatusCode == http.StatusOK {
+			break
+		}
+
+		// Rate limit - retry with exponential backoff
+		if resp.StatusCode == http.StatusTooManyRequests && attempt < maxRetries-1 {
+			resp.Body.Close()
+			backoff := time.Duration(1<<uint(attempt)) * time.Second // 1s, 2s, 4s
+			time.Sleep(backoff)
+			continue
+		}
+
+		// Other errors - return immediately
+		body, _ := io.ReadAll(resp.Body)
+		resp.Body.Close()
+		return nil, fmt.Errorf("Drive API error (status %d): %s", resp.StatusCode, string(body))
+	}
+
+	defer resp.Body.Close()
+
+	// Parse response
+	var result struct {
+		StorageQuota struct {
+			Limit string `json:"limit"` // Can be string or number
+			Usage string `json:"usage"`
+		} `json:"storageQuota"`
+	}
+
+	if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
+		return nil, fmt.Errorf("failed to decode response: %w", err)
+	}
+
+	// Parse limit and usage (handle both string and number formats)
+	var limit, usage int64
+	if result.StorageQuota.Limit != "" {
+		fmt.Sscanf(result.StorageQuota.Limit, "%d", &limit)
+	}
+	if result.StorageQuota.Usage != "" {
+		fmt.Sscanf(result.StorageQuota.Usage, "%d", &usage)
+	}
+
+	return &DriveStorageInfo{
+		Limit: limit,
+		Usage: usage,
+	}, nil
+}