feat: 实现多部分上传功能，支持初始化、上传部分、完成和中止上传，添加媒体资产删除功能

backend/providers/storage/provider.go

@@ -6,6 +6,8 @@ import (
 	"encoding/hex"
 	"fmt"
 	"net/url"
+	"os"
+	"path/filepath"
 	"strconv"
 	"time"
 
@@ -39,6 +41,19 @@ type Storage struct {
 	Config *Config
 }
 
+func (s *Storage) Delete(key string) error {
+	if s.Config.Type == "local" {
+		localPath := s.Config.LocalPath
+		if localPath == "" {
+			localPath = "./storage"
+		}
+		path := filepath.Join(localPath, key)
+		return os.Remove(path)
+	}
+	// TODO: S3 implementation
+	return nil
+}
+
 func (s *Storage) SignURL(method, key string, expires time.Duration) (string, error) {
 	exp := time.Now().Add(expires).Unix()
 	sign := s.signature(method, key, exp)