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/app/http/v1/dto/upload.go

@@ -0,0 +1,24 @@
+package dto
+
+type UploadInitForm struct {
+	Hash     string `json:"hash"`
+	Size     int64  `json:"size"`
+	Filename string `json:"filename"`
+	MimeType string `json:"mime_type"`
+	Type     string `json:"type"`
+}
+
+type UploadInitResponse struct {
+	UploadID string `json:"upload_id"`
+	Key      string `json:"key"` // For S3 direct
+	ChunkSize int64 `json:"chunk_size"`
+}
+
+type UploadPartForm struct {
+	UploadID   string `form:"upload_id"`
+	PartNumber int    `form:"part_number"`
+}
+
+type UploadCompleteForm struct {
+	UploadID string `json:"upload_id"`
+}