feat(account): 优化批量更新实现，使用统一 SQL 合并 JSONB 字段

- 新增 BulkUpdate 仓储方法，使用单条 SQL 更新所有账户
- credentials/extra 使用 COALESCE(...) || ? 合并，只更新传入的 key
- name/proxy_id/concurrency/priority/status 只在提供时更新
- 分组绑定仍逐账号处理（需要独立操作）
- 前端优化：Base URL 留空则不修改，按勾选字段更新
- 完善 i18n 文案：说明留空不修改、批量更新行为

backend/internal/repository/account_repo.go

@@ -5,9 +5,11 @@ import (
 	"errors"
 	"github.com/Wei-Shaw/sub2api/internal/model"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/pagination"
+	"github.com/Wei-Shaw/sub2api/internal/service/ports"
 	"time"
 
 	"gorm.io/gorm"
+	"gorm.io/gorm/clause"
 )
 
 type AccountRepository struct {
@@ -352,3 +354,47 @@ func (r *AccountRepository) UpdateExtra(ctx context.Context, id int64, updates m
 	return r.db.WithContext(ctx).Model(&model.Account{}).Where("id = ?", id).
 		Update("extra", account.Extra).Error
 }
+
+// BulkUpdate updates multiple accounts with the provided fields.
+// It merges credentials/extra JSONB fields instead of overwriting them.
+func (r *AccountRepository) BulkUpdate(ctx context.Context, ids []int64, updates ports.AccountBulkUpdate) (int64, error) {
+	if len(ids) == 0 {
+		return 0, nil
+	}
+
+	updateMap := map[string]any{}
+
+	if updates.Name != nil {
+		updateMap["name"] = *updates.Name
+	}
+	if updates.ProxyID != nil {
+		updateMap["proxy_id"] = updates.ProxyID
+	}
+	if updates.Concurrency != nil {
+		updateMap["concurrency"] = *updates.Concurrency
+	}
+	if updates.Priority != nil {
+		updateMap["priority"] = *updates.Priority
+	}
+	if updates.Status != nil {
+		updateMap["status"] = *updates.Status
+	}
+	if len(updates.Credentials) > 0 {
+		updateMap["credentials"] = gorm.Expr("COALESCE(credentials,'{}') || ?", updates.Credentials)
+	}
+	if len(updates.Extra) > 0 {
+		updateMap["extra"] = gorm.Expr("COALESCE(extra,'{}') || ?", updates.Extra)
+	}
+
+	if len(updateMap) == 0 {
+		return 0, nil
+	}
+
+	result := r.db.WithContext(ctx).
+		Model(&model.Account{}).
+		Where("id IN ?", ids).
+		Clauses(clause.Returning{}).
+		Updates(updateMap)
+
+	return result.RowsAffected, result.Error
+}