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_test.go

@@ -0,0 +1,179 @@
+package service
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"with_you/internal/model"
+	"with_you/internal/repository"
+)
+
+// stubGroupRepo 通过嵌入 repository.GroupRepository 接口（保持 nil），
+// 仅覆盖测试涉及的方法。未覆盖的方法被调用时会 panic——这能在测试中
+// 提前暴露「Service 调用了非预期 repo 方法」的回归。
+type stubGroupRepo struct {
+	repository.GroupRepository // nil 嵌入，未覆盖方法 panic
+
+	groupByID     map[string]*model.Group
+	groupByIDErr  error
+	memberByUser  map[string]*model.GroupMember
+	memberErr     error
+	transferCalls []transferCall
+	transferErr   error
+}
+
+type transferCall struct {
+	GroupID, OldOwner, NewOwner string
+}
+
+func (s *stubGroupRepo) GetByID(id string) (*model.Group, error) {
+	if s.groupByIDErr != nil {
+		return nil, s.groupByIDErr
+	}
+	g, ok := s.groupByID[id]
+	if !ok {
+		return nil, errors.New("not found")
+	}
+	return g, nil
+}
+
+func (s *stubGroupRepo) GetMember(groupID, userID string) (*model.GroupMember, error) {
+	if s.memberErr != nil {
+		return nil, s.memberErr
+	}
+	m, ok := s.memberByUser[userID]
+	if !ok {
+		return nil, errors.New("not member")
+	}
+	return m, nil
+}
+
+func (s *stubGroupRepo) TransferOwner(groupID, oldOwnerID, newOwnerID string) error {
+	s.transferCalls = append(s.transferCalls, transferCall{
+		GroupID: groupID, OldOwner: oldOwnerID, NewOwner: newOwnerID,
+	})
+	// 模拟真实 DB 语义：事务提交后 owner_id 已变更，后续 GetByID 读到新值
+	if g, ok := s.groupByID[groupID]; ok {
+		g.OwnerID = newOwnerID
+	}
+	return s.transferErr
+}
+
+// stubUserRepo 同样仅覆盖 GetByID。
+type stubUserRepo struct {
+	repository.UserRepository // nil 嵌入
+
+	byID map[string]*model.User
+}
+
+func (s *stubUserRepo) GetByID(id string) (*model.User, error) {
+	u, ok := s.byID[id]
+	if !ok {
+		return nil, errors.New("not found")
+	}
+	return u, nil
+}
+
+// TestTransferOwner_Success 正常转让：TransferOwner 应被调用一次，
+// 参数为 (groupID, 当前 owner, 新 owner)。
+func TestTransferOwner_Success(t *testing.T) {
+	repo := &stubGroupRepo{
+		groupByID: map[string]*model.Group{
+			"g1": {ID: "g1", OwnerID: "old-owner", Name: "测试群"},
+		},
+		memberByUser: map[string]*model.GroupMember{
+			"old-owner": {UserID: "old-owner", GroupID: "g1", Role: model.GroupRoleOwner},
+			"new-owner": {UserID: "new-owner", GroupID: "g1", Role: model.GroupRoleMember},
+		},
+	}
+	userRepo := &stubUserRepo{
+		byID: map[string]*model.User{
+			"new-owner": {ID: "new-owner", Username: "new", Nickname: "新群主"},
+		},
+	}
+	svc := NewAdminGroupService(repo, userRepo)
+
+	resp, err := svc.TransferOwner(context.Background(), "g1", "new-owner")
+	if err != nil {
+		t.Fatalf("TransferOwner failed: %v", err)
+	}
+
+	// 校验 TransferOwner 恰好被调用一次，参数正确
+	if len(repo.transferCalls) != 1 {
+		t.Fatalf("expected 1 TransferOwner call, got %d", len(repo.transferCalls))
+	}
+	tc := repo.transferCalls[0]
+	if tc.GroupID != "g1" || tc.OldOwner != "old-owner" || tc.NewOwner != "new-owner" {
+		t.Errorf("TransferOwner called with (%s,%s,%s), want (g1,old-owner,new-owner)",
+			tc.GroupID, tc.OldOwner, tc.NewOwner)
+	}
+
+	// 响应应反映新群主
+	if resp == nil {
+		t.Fatal("expected non-nil response")
+	}
+	if resp.OwnerID != "new-owner" {
+		t.Errorf("response OwnerID = %s, want new-owner", resp.OwnerID)
+	}
+}
+
+// TestTransferOwner_NewOwnerNotMember 新群主非成员时应返回错误，
+// 且 TransferOwner 不应被调用。
+func TestTransferOwner_NewOwnerNotMember(t *testing.T) {
+	repo := &stubGroupRepo{
+		groupByID: map[string]*model.Group{
+			"g1": {ID: "g1", OwnerID: "old-owner"},
+		},
+		memberByUser: map[string]*model.GroupMember{
+			"old-owner": {UserID: "old-owner", GroupID: "g1", Role: model.GroupRoleOwner},
+			// new-owner 不在成员表
+		},
+	}
+	svc := NewAdminGroupService(repo, &stubUserRepo{})
+
+	_, err := svc.TransferOwner(context.Background(), "g1", "new-owner")
+	if err == nil {
+		t.Fatal("expected error when new owner is not a member")
+	}
+	if len(repo.transferCalls) != 0 {
+		t.Errorf("TransferOwner should not be called, got %d calls", len(repo.transferCalls))
+	}
+}
+
+// TestTransferOwner_GroupNotFound 群不存在时应返回错误。
+func TestTransferOwner_GroupNotFound(t *testing.T) {
+	repo := &stubGroupRepo{
+		groupByID: map[string]*model.Group{}, // g1 不存在
+	}
+	svc := NewAdminGroupService(repo, &stubUserRepo{})
+
+	_, err := svc.TransferOwner(context.Background(), "g1", "new-owner")
+	if err == nil {
+		t.Fatal("expected error when group does not exist")
+	}
+	if len(repo.transferCalls) != 0 {
+		t.Errorf("TransferOwner should not be called, got %d calls", len(repo.transferCalls))
+	}
+}
+
+// TestTransferOwner_AlreadyOwner 新群主已是群主时应拒绝（无操作幂等）。
+func TestTransferOwner_AlreadyOwner(t *testing.T) {
+	repo := &stubGroupRepo{
+		groupByID: map[string]*model.Group{
+			"g1": {ID: "g1", OwnerID: "same-user"},
+		},
+		memberByUser: map[string]*model.GroupMember{
+			"same-user": {UserID: "same-user", GroupID: "g1", Role: model.GroupRoleOwner},
+		},
+	}
+	svc := NewAdminGroupService(repo, &stubUserRepo{})
+
+	_, err := svc.TransferOwner(context.Background(), "g1", "same-user")
+	if err == nil {
+		t.Fatal("expected error when transferring to existing owner")
+	}
+	if len(repo.transferCalls) != 0 {
+		t.Errorf("TransferOwner should not be called, got %d calls", len(repo.transferCalls))
+	}
+}