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/post_repo.go

@@ -529,3 +529,115 @@ func (r *PostRepository) deleteWithTx(tx *gorm.DB, id string) error {
 	// 最后删除帖子本身（软删除）
 	return tx.Delete(&model.Post{}, "id = ?", id).Error
 }
+
+// ========== Admin methods ==========
+
+// AdminPostListQuery 管理端帖子列表查询参数
+type AdminPostListQuery struct {
+	Page      int
+	PageSize  int
+	Keyword   string
+	Status    string // 为空表示所有状态
+	AuthorID  string
+	StartDate string // 格式: 2006-01-02
+	EndDate   string // 格式: 2006-01-02
+}
+
+// AdminList 管理端分页获取帖子列表（支持多条件筛选）
+func (r *PostRepository) AdminList(query AdminPostListQuery) ([]*model.Post, int64, error) {
+	var posts []*model.Post
+	var total int64
+
+	db := r.db.Model(&model.Post{})
+
+	// 关键词搜索（标题或内容）
+	if query.Keyword != "" {
+		if r.db.Dialector.Name() == "postgres" {
+			db = db.Where(
+				"to_tsvector('simple', COALESCE(title, '') || ' ' || COALESCE(content, '')) @@ plainto_tsquery('simple', ?)",
+				query.Keyword,
+			)
+		} else {
+			searchPattern := "%" + query.Keyword + "%"
+			db = db.Where("title LIKE ? OR content LIKE ?", searchPattern, searchPattern)
+		}
+	}
+
+	// 状态筛选
+	if query.Status != "" {
+		db = db.Where("status = ?", query.Status)
+	}
+
+	// 作者筛选
+	if query.AuthorID != "" {
+		db = db.Where("user_id = ?", query.AuthorID)
+	}
+
+	// 日期范围筛选
+	if query.StartDate != "" {
+		db = db.Where("created_at >= ?", query.StartDate+" 00:00:00")
+	}
+	if query.EndDate != "" {
+		db = db.Where("created_at <= ?", query.EndDate+" 23:59:59")
+	}
+
+	// 统计总数
+	db.Count(&total)
+
+	// 分页查询
+	offset := (query.Page - 1) * query.PageSize
+	err := db.Preload("User").Preload("Images").
+		Offset(offset).Limit(query.PageSize).
+		Order("created_at DESC").
+		Find(&posts).Error
+
+	return posts, total, err
+}
+
+// GetByIDForAdmin 管理端根据ID获取帖子（包含所有状态）
+func (r *PostRepository) GetByIDForAdmin(id string) (*model.Post, error) {
+	var post model.Post
+	err := r.db.Preload("User").Preload("Images").First(&post, "id = ?", id).Error
+	if err != nil {
+		return nil, err
+	}
+	return &post, nil
+}
+
+// BatchDelete 批量删除帖子
+func (r *PostRepository) BatchDelete(ids []string) ([]string, error) {
+	var failedIDs []string
+
+	for _, id := range ids {
+		if err := r.Delete(id); err != nil {
+			failedIDs = append(failedIDs, id)
+		}
+	}
+
+	return failedIDs, nil
+}
+
+// BatchUpdateStatus 批量更新帖子审核状态
+func (r *PostRepository) BatchUpdateStatus(ids []string, status model.PostStatus, reviewedBy string) ([]string, error) {
+	var failedIDs []string
+
+	for _, id := range ids {
+		if err := r.UpdateModerationStatus(id, status, "", reviewedBy); err != nil {
+			failedIDs = append(failedIDs, id)
+		}
+	}
+
+	return failedIDs, nil
+}
+
+// UpdatePinStatus 更新帖子置顶状态
+func (r *PostRepository) UpdatePinStatus(postID string, isPinned bool) error {
+	return r.db.Model(&model.Post{}).Where("id = ?", postID).
+		Update("is_pinned", isPinned).Error
+}
+
+// UpdateFeatureStatus 更新帖子加精状态
+func (r *PostRepository) UpdateFeatureStatus(postID string, isFeatured bool) error {
+	return r.db.Model(&model.Post{}).Where("id = ?", postID).
+		Update("is_featured", isFeatured).Error
+}