feat(usage): 在 /admin/usage 支持查看已删除用户的历史使用情况

用户软删除后使用记录仍在,但身份(邮箱)被 ent 软删除拦截器隐藏。本次在
三条管理员只读路径定点穿透软删除过滤,并把删除状态传播到前端标记,零新表/
迁移/回填:

- 后端穿透:富化 usage 日志(loadUsers)、用户搜索(ListWithFilters +
  UserListFilters.IncludeDeleted)、点击详情(GetByIDIncludeDeleted /
  GetUserIncludeDeleted + getById ?include_deleted 分支)
- 状态传播:service.User / dto.User 新增 DeletedAt;SearchUsers 标记 deleted
- 前端:表格与余额弹窗展示"已删除"徽标、筛选下拉标注并排序、点击走
  include_deleted;新增 i18n admin.usage.userDeletedBadge
- 安全:普通用户 usage 仅查本人(无 PII 泄漏);主用户列表与默认 getById
  行为不变(已删用户仍 404);仅 admin 搜索设 IncludeDeleted

后端 build / 三态 vet / unit 全量 / 仓储集成全绿;前端 typecheck / vitest /
改动文件 eslint 全清。

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/internal/handler/admin/usage_handler.go

@@ -344,23 +344,25 @@ func (h *UsageHandler) SearchUsers(c *gin.Context) {
 	}
 
 	// Limit to 30 results
-	users, _, err := h.adminService.ListUsers(c.Request.Context(), 1, 30, service.UserListFilters{Search: keyword}, "email", "asc")
+	users, _, err := h.adminService.ListUsers(c.Request.Context(), 1, 30, service.UserListFilters{Search: keyword, IncludeDeleted: true}, "email", "asc")
 	if err != nil {
 		response.ErrorFrom(c, err)
 		return
 	}
 
-	// Return simplified user list (only id and email)
+	// Return simplified user list (only id, email and deleted flag)
 	type SimpleUser struct {
-		ID    int64  `json:"id"`
-		Email string `json:"email"`
+		ID      int64  `json:"id"`
+		Email   string `json:"email"`
+		Deleted bool   `json:"deleted"`
 	}
 
 	result := make([]SimpleUser, len(users))
 	for i, u := range users {
 		result[i] = SimpleUser{
-			ID:    u.ID,
-			Email: u.Email,
+			ID:      u.ID,
+			Email:   u.Email,
+			Deleted: u.DeletedAt != nil,
 		}
 	}