fix: golangci-lint 零告警通过 (57→0) + gofumpt/goimports 全量格式化

## CI 修复 (P0/P1)

P0 — 编译阻塞:
  - interfaces.go: postUseCase ISP 接口移除不用的 Create/Update/Delete

P1 — 必须修复:
  - ST1000: 为 13 个包添加包注释 (common/config/model/service/...)
  - ST1005: redis_store.go 全部错误消息改为小写开头
  - errcheck (19处): defer Close()→闭包忽略, notifier.Create→_=, r.Run→检查error
  - errorlint (9处): switch-on-error→errors.Is 链, ==→errors.Is
  - ST1020/ST1022: 导出符号注释以符号名开头

P2 — 安全评审:
  - gosec (12处): G203/G301/G304/G306 添加 nolint 注释并附理由

P3 — 清理:
  - unused: 移除 hasUnicode/energyStore/current/energyAdminUseCase
  - gofumpt + goimports 全量格式化 (35+ 文件)

internal/repository/announcement_repo.go

@@ -1,3 +1,4 @@
+// Package repository 提供基于 GORM 的数据访问层实现。
 package repository
 
 import (

internal/repository/comment_mention_repo.go

@@ -73,7 +73,8 @@ func (r *CommentRepo) SearchUsersByLevel(keyword string, minLevel, limit int, fo
 	Username string
 	Avatar   string
 	Exp      int
-}, error) {
+}, error,
+) {
 	type result struct {
 		UID      uint
 		Username string

internal/repository/comment_repo.go

@@ -161,7 +161,7 @@ func (r *CommentRepo) DecrCommentsCount(postID uint) error {
 		UpdateColumn("comments_count", gorm.Expr("GREATEST(comments_count - 1, 0)")).Error
 }
 
-// CountRepliesByRootByStatus 统计某条顶级评论的回复数（可选是否统计已删除）
+// CountRepliesByRoot 统计某条顶级评论的回复数（可选是否统计已删除）
 func (r *CommentRepo) CountRepliesByRoot(rootID uint, includeDeleted bool) (int, error) {
 	var count int64
 	q := r.db.Model(&model.Comment{}).Where("root_id = ? AND parent_id IS NOT NULL", rootID)

internal/repository/reaction_repo.go

@@ -1,6 +1,8 @@
 package repository
 
 import (
+	"errors"
+
 	"metazone.cc/mce/internal/model"
 	"metazone.cc/mce/internal/service"
 
@@ -103,7 +105,7 @@ func (r *ReactionRepo) GetPostAuthorID(postID uint) (uint, error) {
 func (r *ReactionRepo) UpsertDailyLikeSummary(authorUID uint, date string, likerUID string) error {
 	var existing model.DailyLikeSummary
 	err := r.db.Where("author_uid = ? AND date = ?", authorUID, date).First(&existing).Error
-	if err == gorm.ErrRecordNotFound {
+	if errors.Is(err, gorm.ErrRecordNotFound) {
 		return r.db.Create(&model.DailyLikeSummary{
 			AuthorUID: authorUID,
 			Date:      date,

internal/repository/tag_repo.go

@@ -1,6 +1,8 @@
 package repository
 
 import (
+	"errors"
+
 	"metazone.cc/mce/internal/model"
 	"metazone.cc/mce/internal/service"
 
@@ -29,7 +31,7 @@ func (r *TagRepo) FindOrCreate(name, slug string) (*model.Tag, error) {
 	if err == nil {
 		return &tag, nil
 	}
-	if err != gorm.ErrRecordNotFound {
+	if err != nil && !errors.Is(err, gorm.ErrRecordNotFound) {
 		return nil, err
 	}
 	tag = model.Tag{Name: name, Slug: slug}

internal/repository/user_repo.go

@@ -151,4 +151,3 @@ func (r *UserRepo) CountSearchUsers(keyword, role, status string) (int64, error)
 	err := r.buildSearchQuery(keyword, role, status).Count(&count).Error
 	return count, err
 }
-