feat(admin): add comprehensive admin management system

- Add admin handlers and services for users, posts, comments, groups, and dashboard
- Implement role permission management with ability to view and update permissions
- Add database seeding for roles and Casbin permission policies
- Upgrade Casbin from v2 to v3 with GORM adapter for persistent policy storage
- Add admin-specific repository methods with filtering and pagination
- Register new admin API routes under /api/v1/admin/*

internal/repository/user_repo.go

@@ -403,3 +403,53 @@ func (r *UserRepository) GetMutualFollowStatus(currentUserID string, targetUserI
 
 	return result, nil
 }
+
+// AdminList 管理端分页获取用户列表（支持关键词和状态筛选）
+func (r *UserRepository) AdminList(page, pageSize int, keyword, status string) ([]*model.User, int64, error) {
+	var users []*model.User
+	var total int64
+
+	query := r.db.Model(&model.User{})
+
+	// 关键词搜索（用户名、昵称、邮箱）
+	if keyword != "" {
+		if r.db.Dialector.Name() == "postgres" {
+			query = query.Where(
+				"username ILIKE ? OR nickname ILIKE ? OR email ILIKE ?",
+				"%"+keyword+"%", "%"+keyword+"%", "%"+keyword+"%",
+			)
+		} else {
+			lowerSearchPattern := "%" + strings.ToLower(keyword) + "%"
+			query = query.Where(
+				"LOWER(username) LIKE ? OR LOWER(nickname) LIKE ? OR LOWER(email) LIKE ?",
+				lowerSearchPattern, lowerSearchPattern, lowerSearchPattern,
+			)
+		}
+	}
+
+	// 状态筛选
+	if status != "" {
+		query = query.Where("status = ?", status)
+	}
+
+	query.Count(&total)
+
+	offset := (page - 1) * pageSize
+	err := query.Order("created_at DESC, id DESC").Offset(offset).Limit(pageSize).Find(&users).Error
+
+	return users, total, err
+}
+
+// GetCommentsCount 获取用户评论数
+func (r *UserRepository) GetCommentsCount(userID string) (int64, error) {
+	var count int64
+	err := r.db.Model(&model.Comment{}).
+		Where("user_id = ?", userID).
+		Count(&count).Error
+	return count, err
+}
+
+// UpdateStatus 更新用户状态
+func (r *UserRepository) UpdateStatus(userID string, status model.UserStatus) error {
+	return r.db.Model(&model.User{}).Where("id = ?", userID).Update("status", status).Error
+}