feat(auth): 用户/角色模型与数据访问层

- constants: 用户状态、性别、角色代码常量定义
- model: User/Role/UserRole GORM 模型
- dao: UserDAO (CRUD + 账号查询) + RoleDAO (角色分配/查询/检查)
- provider: Auth 模块 Wire Provider Set

Made-with: Cursor

backend/go-service/app/auth/provider.go

@@ -0,0 +1,13 @@
+// Package auth 提供用户认证与授权模块
+package auth
+
+import (
+	"github.com/echochat/backend/app/auth/dao"
+	"github.com/google/wire"
+)
+
+// AuthSet Auth 模块依赖注入 Provider Set
+var AuthSet = wire.NewSet(
+	dao.NewUserDAO,
+	dao.NewRoleDAO,
+)