refactor(server): decouple services and improve architecture

- Introduce interfaces for all major services (JWT, PostAI, Comment, Message, Notification, QRCodeLogin, Upload, Vote, etc.) to support dependency inversion.
- Move query parameters from `internal/dto` to a new `internal/query` package to separate request payloads from data transfer objects.
- Refactor `internal/router` to use embedded `RouterDeps` for cleaner dependency management.
- Decouple handlers from repositories by injecting services instead of direct repository access, ensuring proper layering.
- Improve database initialization by moving it from `internal/model` to `internal/database`.
- Optimize message decryption by implementing a more efficient `BatchDecrypt` method in `MessageEncryptor` using a worker pool.
- Enhance error handling and security by implementing fail-fast checks for encryption key length during startup.
- Clean up unused code, including the `avatar` package and several unused DTOs.

internal/service/admin_group_service.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 
 	"with_you/internal/dto"
+	apperrors "with_you/internal/errors"
 	"with_you/internal/model"
 	"with_you/internal/repository"
 )
@@ -291,48 +292,36 @@ func (s *adminGroupServiceImpl) RemoveMember(ctx context.Context, groupID string
 }
 
 // TransferOwner 转让群主
+// 委托 groupRepo.TransferOwner 在单个数据库事务内原子完成：
+//   - 更新 group.owner_id 为新群主
+//   - 原群主角色降级为普通成员
+//   - 新群主角色升级为 owner
+//
+// 任何一步失败都会整体回滚，避免出现「两个群主」或「零群主」的数据不一致。
 func (s *adminGroupServiceImpl) TransferOwner(ctx context.Context, groupID string, newOwnerID string) (*dto.AdminGroupDetailResponse, error) {
-	// 先检查群组是否存在
+	// 校验群组存在
 	group, err := s.groupRepo.GetByID(groupID)
 	if err != nil {
-		return nil, errors.New("群组不存在")
+		return nil, apperrors.ErrGroupNotFound
 	}
 
-	// 检查新群主是否是群成员
+	// 校验新群主是群成员
 	newOwnerMember, err := s.groupRepo.GetMember(groupID, newOwnerID)
 	if err != nil {
-		return nil, errors.New("新群主不是群组成员")
+		return nil, apperrors.ErrNotGroupMember
+	}
+	// 新群主已是群主则无需转让
+	if newOwnerMember.Role == model.GroupRoleOwner {
+		return nil, apperrors.ErrInvalidOperation
 	}
 
-	// 获取当前群主信息
-	currentOwnerMember, err := s.groupRepo.GetMember(groupID, group.OwnerID)
-	if err != nil {
-		return nil, errors.New("当前群主信息不存在")
+	// 校验当前群主信息存在
+	if _, err := s.groupRepo.GetMember(groupID, group.OwnerID); err != nil {
+		return nil, apperrors.ErrGroupNotFound
 	}
 
-	oldOwnerID := group.OwnerID
-
-	// 更新当前群主为普通成员
-	err = s.groupRepo.SetMemberRole(groupID, oldOwnerID, model.GroupRoleMember)
-	if err != nil {
-		return nil, err
-	}
-
-	// 更新新群主角色
-	err = s.groupRepo.SetMemberRole(groupID, newOwnerID, model.GroupRoleOwner)
-	if err != nil {
-		// 回滚
-		_ = s.groupRepo.SetMemberRole(groupID, oldOwnerID, model.GroupRoleOwner)
-		return nil, err
-	}
-
-	// 更新群组的OwnerID
-	group.OwnerID = newOwnerID
-	err = s.groupRepo.Update(group)
-	if err != nil {
-		// 回滚
-		_ = s.groupRepo.SetMemberRole(groupID, oldOwnerID, model.GroupRoleOwner)
-		_ = s.groupRepo.SetMemberRole(groupID, newOwnerID, newOwnerMember.Role)
+	// 原子转让：所有写入在 groupRepo.TransferOwner 的单个事务内完成
+	if err := s.groupRepo.TransferOwner(groupID, group.OwnerID, newOwnerID); err != nil {
 		return nil, err
 	}
 
@@ -373,7 +362,5 @@ func (s *adminGroupServiceImpl) TransferOwner(ctx context.Context, groupID strin
 		}
 	}
 
-	_ = currentOwnerMember // 避免 unused variable 警告
-
 	return response, nil
 }