feat: 分类系统 + 标签系统 — Phase 4 完成

分类：Model/Repo/Service/Controller + 管理后台树形页面 + 首页导航栏
标签：Model/Repo/Service/Controller + /tags/{slug} 落地页 + 写文章页输入
Post 加 CategoryID，Create/Update 支持分类和标签
SQL 迁移含 categories/tags/post_tags 表及预设未分类

internal/service/category_service.go

@@ -0,0 +1,75 @@
+package service
+
+import "metazone.cc/mce/internal/model"
+
+// CategoryStore 分类仓库接口（ISP）
+type CategoryStore interface {
+	Create(c *model.Category) error
+	Update(c *model.Category) error
+	Delete(id uint) error
+	FindByID(id uint) (*model.Category, error)
+	ListAll() ([]model.Category, error)
+	GetLeaves() ([]model.Category, error)
+}
+
+// CategoryService 分类业务逻辑
+type CategoryService struct {
+	repo CategoryStore
+}
+
+// NewCategoryService 构造函数
+func NewCategoryService(repo CategoryStore) *CategoryService {
+	return &CategoryService{repo: repo}
+}
+
+// Create 创建分类
+func (s *CategoryService) Create(c *model.Category) error {
+	return s.repo.Create(c)
+}
+
+// Update 更新分类
+func (s *CategoryService) Update(c *model.Category) error {
+	return s.repo.Update(c)
+}
+
+// Delete 删除分类
+func (s *CategoryService) Delete(id uint) error {
+	return s.repo.Delete(id)
+}
+
+// Tree 获取两级分类树
+func (s *CategoryService) Tree() ([]model.Category, error) {
+	all, err := s.repo.ListAll()
+	if err != nil {
+		return nil, err
+	}
+	// 构建树：parent_id=nil 的为根节点
+	parentMap := make(map[uint]*model.Category)
+	var roots []*model.Category
+	for i := range all {
+		c := &all[i]
+		c.Children = []model.Category{}
+		parentMap[c.ID] = c
+		if c.ParentID == nil {
+			roots = append(roots, c)
+		}
+	}
+	for i := range all {
+		c := &all[i]
+		if c.ParentID != nil {
+			if parent, ok := parentMap[*c.ParentID]; ok {
+				parent.Children = append(parent.Children, *c)
+			}
+		}
+	}
+	result := make([]model.Category, len(roots))
+	for i, r := range roots {
+		result[i] = *r
+	}
+	return result, nil
+}
+
+// GetLeaves 获取所有叶子分类（用于写文章页下拉选择）
+func (s *CategoryService) GetLeaves() ([]model.Category, error) {
+	return s.repo.GetLeaves()
+}

internal/service/post_audit_service.go

@@ -1,12 +1,14 @@
 package service
 
 import (
+	"strconv"
+
 	"metazone.cc/mce/internal/common"
 	"metazone.cc/mce/internal/model"
 )
 
 // Update 编辑帖子（权限在 controller 层检查）
-func (s *PostService) Update(postID uint, title, body string, visibility, postType, reprintSource, declaration string, reprintProhibited bool) error {
+func (s *PostService) Update(postID uint, title, body string, visibility, postType, reprintSource, declaration string, reprintProhibited bool, categoryID string) error {
 	post, err := s.findPost(postID)
 	if err != nil {
 		return err
@@ -22,6 +24,13 @@ func (s *PostService) Update(postID uint, title, body string, visibility, postTy
 	post.ReprintSource = reprintSource
 	post.Declaration = declaration
 	post.ReprintProhibited = reprintProhibited
+	// 分类
+	if cid, err := strconv.ParseUint(categoryID, 10, 64); err == nil && cid > 0 {
+		id := uint(cid)
+		post.CategoryID = &id
+	} else {
+		post.CategoryID = nil
+	}
 
 	// 已通过帖子：编辑内容保存为待审修订，不影响当前展示
 	if post.Status == model.PostStatusApproved {

internal/service/post_service.go

@@ -3,6 +3,7 @@ package service
 import (
 	"errors"
 	"fmt"
+	"strconv"
 	"time"
 
 	"metazone.cc/mce/internal/common"
@@ -68,7 +69,7 @@ func (s *PostService) findPostWithAuthor(id uint) (*model.Post, error) {
 // Create 创建帖子
 // body 为 Vditor 输出的 Markdown，后端直接存储不做 HTML 消毒
 // MD 是纯文本，无 XSS 注入风险；前端渲染时由 Vditor 转 HTML
-func (s *PostService) Create(userID uint, title, body string, visibility, postType, reprintSource, declaration string, reprintProhibited bool) (*model.Post, error) {
+func (s *PostService) Create(userID uint, title, body string, visibility, postType, reprintSource, declaration string, reprintProhibited bool, categoryID string) (*model.Post, error) {
 	status := model.PostStatusApproved
 	if s.auditEnabled() {
 		status = model.PostStatusDraft
@@ -87,6 +88,11 @@ func (s *PostService) Create(userID uint, title, body string, visibility, postTy
 		Declaration:       declaration,
 		ReprintProhibited: reprintProhibited,
 	}
+	// 解析分类 ID
+	if cid, err := strconv.ParseUint(categoryID, 10, 64); err == nil && cid > 0 {
+		id := uint(cid)
+		post.CategoryID = &id
+	}
 	if err := s.repo.Create(post); err != nil {
 		return nil, err
 	}

internal/service/tag_service.go

@@ -0,0 +1,82 @@
+package service
+
+import (
+	"regexp"
+	"strings"
+
+	"metazone.cc/mce/internal/model"
+)
+
+// TagStore 标签仓库接口（ISP）
+type TagStore interface {
+	FindOrCreate(name, slug string) (*model.Tag, error)
+	FindBySlug(slug string) (*model.Tag, error)
+	SetPostTags(postID uint, tagIDs []uint) error
+	GetPostTags(postID uint) ([]model.Tag, error)
+	GetPostsByTag(tagID uint, offset, limit int) ([]model.Post, int64, error)
+}
+
+var slugRegex = regexp.MustCompile(`[^a-z0-9\-]`)
+
+// TagService 标签业务逻辑
+type TagService struct {
+	repo TagStore
+}
+
+// NewTagService 构造函数
+func NewTagService(repo TagStore) *TagService {
+	return &TagService{repo: repo}
+}
+
+// ParseAndSave 解析标签名列表（逗号分隔），查找或创建，返回 tagID 列表
+func (s *TagService) ParseAndSave(tagStr string) ([]uint, error) {
+	if strings.TrimSpace(tagStr) == "" {
+		return nil, nil
+	}
+	names := strings.Split(tagStr, ",")
+	var tagIDs []uint
+	seen := make(map[string]bool)
+	for _, name := range names {
+		name = strings.TrimSpace(name)
+		if name == "" || len(name) > 50 {
+			continue
+		}
+		slug := slugify(name)
+		if seen[slug] {
+			continue
+		}
+		seen[slug] = true
+		tag, err := s.repo.FindOrCreate(name, slug)
+		if err != nil {
+			return nil, err
+		}
+		tagIDs = append(tagIDs, tag.ID)
+	}
+	return tagIDs, nil
+}
+
+// SetPostTags 解析标签字符串并关联到文章
+func (s *TagService) SetPostTags(postID uint, tagStr string) error {
+	tagIDs, err := s.ParseAndSave(tagStr)
+	if err != nil {
+		return err
+	}
+	return s.repo.SetPostTags(postID, tagIDs)
+}
+
+// GetPostsByTag 按标签分页查询文章
+func (s *TagService) GetPostsByTag(slug string, page, pageSize int) ([]model.Post, int64, *model.Tag, error) {
+	tag, err := s.repo.FindBySlug(slug)
+	if err != nil {
+		return nil, 0, nil, err
+	}
+	offset := (page - 1) * pageSize
+	posts, total, err := s.repo.GetPostsByTag(tag.ID, offset, pageSize)
+	return posts, total, tag, err
+}
+
+func slugify(name string) string {
+	s := strings.ToLower(strings.TrimSpace(name))
+	s = strings.ReplaceAll(s, " ", "-")
+	return slugRegex.ReplaceAllString(s, "")
+}