refactor: introduce Wire dependency injection and interface-based architecture

- Add Google Wire for compile-time dependency injection
- Replace concrete service types with interfaces across handlers
- Remove global state (DB, cache) in favor of constructor injection
- Split monolithic files into focused modules:
  - config: separate files for each config domain
  - dto: converters split by domain (user, post, message, group)
  - cache: separate metrics.go and redis_cache.go
- Introduce unified apperrors package with string-based error codes
- Add transaction support with context-aware repository methods
- Upgrade golang.org/x/crypto from 0.17.0 to 0.26.0

internal/repository/post_repo.go

@@ -2,6 +2,7 @@ package repository
 
 import (
 	"carrot_bbs/internal/model"
+	"context"
 	"time"
 
 	"gorm.io/gorm"
@@ -17,6 +18,14 @@ func NewPostRepository(db *gorm.DB) *PostRepository {
 	return &PostRepository{db: db}
 }
 
+// getDB 获取数据库连接（优先使用 context 中的事务）
+func (r *PostRepository) getDB(ctx context.Context) *gorm.DB {
+	if tx := GetTxFromContext(ctx); tx != nil {
+		return tx
+	}
+	return r.db
+}
+
 // Create 创建帖子
 func (r *PostRepository) Create(post *model.Post, images []string) error {
 	return r.db.Transaction(func(tx *gorm.DB) error {
@@ -419,3 +428,104 @@ func (r *PostRepository) GetByIDs(ids []string) ([]*model.Post, error) {
 
 	return ordered, nil
 }
+
+// ========== Context-aware methods for transaction support ==========
+
+// CreateWithContext 创建帖子（支持事务）
+func (r *PostRepository) CreateWithContext(ctx context.Context, post *model.Post, images []string) error {
+	db := r.getDB(ctx)
+
+	// 如果 context 中有事务，直接使用
+	if tx := GetTxFromContext(ctx); tx != nil {
+		return r.createWithTx(tx, post, images)
+	}
+
+	// 否则开启新事务
+	return db.WithContext(ctx).Transaction(func(tx *gorm.DB) error {
+		return r.createWithTx(tx, post, images)
+	})
+}
+
+// createWithTx 使用指定事务创建帖子
+func (r *PostRepository) createWithTx(tx *gorm.DB, post *model.Post, images []string) error {
+	// 创建帖子
+	if err := tx.Create(post).Error; err != nil {
+		return err
+	}
+
+	// 创建图片记录
+	for i, url := range images {
+		image := &model.PostImage{
+			PostID:    post.ID,
+			URL:       url,
+			SortOrder: i,
+		}
+		if err := tx.Create(image).Error; err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// GetByIDWithContext 根据ID获取帖子（支持事务）
+func (r *PostRepository) GetByIDWithContext(ctx context.Context, id string) (*model.Post, error) {
+	var post model.Post
+	err := r.getDB(ctx).WithContext(ctx).Preload("User").Preload("Images").First(&post, "id = ?", id).Error
+	if err != nil {
+		return nil, err
+	}
+	return &post, nil
+}
+
+// UpdateWithContext 更新帖子（支持事务）
+func (r *PostRepository) UpdateWithContext(ctx context.Context, post *model.Post) error {
+	post.UpdatedAt = time.Now()
+	return r.getDB(ctx).WithContext(ctx).Save(post).Error
+}
+
+// DeleteWithContext 删除帖子（支持事务）
+func (r *PostRepository) DeleteWithContext(ctx context.Context, id string) error {
+	db := r.getDB(ctx)
+
+	// 如果 context 中有事务，直接使用
+	if tx := GetTxFromContext(ctx); tx != nil {
+		return r.deleteWithTx(tx, id)
+	}
+
+	// 否则开启新事务
+	return db.WithContext(ctx).Transaction(func(tx *gorm.DB) error {
+		return r.deleteWithTx(tx, id)
+	})
+}
+
+// deleteWithTx 使用指定事务删除帖子
+func (r *PostRepository) deleteWithTx(tx *gorm.DB, id string) error {
+	// 删除帖子图片
+	if err := tx.Where("post_id = ?", id).Delete(&model.PostImage{}).Error; err != nil {
+		return err
+	}
+
+	// 删除帖子点赞记录
+	if err := tx.Where("post_id = ?", id).Delete(&model.PostLike{}).Error; err != nil {
+		return err
+	}
+
+	// 删除帖子收藏记录
+	if err := tx.Where("post_id = ?", id).Delete(&model.Favorite{}).Error; err != nil {
+		return err
+	}
+
+	// 删除评论点赞记录（子查询获取该帖子所有评论ID）
+	if err := tx.Where("comment_id IN (SELECT id FROM comments WHERE post_id = ?)", id).Delete(&model.CommentLike{}).Error; err != nil {
+		return err
+	}
+
+	// 删除帖子评论
+	if err := tx.Where("post_id = ?", id).Delete(&model.Comment{}).Error; err != nil {
+		return err
+	}
+
+	// 最后删除帖子本身（软删除）
+	return tx.Delete(&model.Post{}, "id = ?", id).Error
+}