feat: implement Model Context Protocol (MCP) server and download manager capabilities

pkg/base/model.go

@@ -124,6 +124,11 @@ type FileInfo struct {
 	Req *Request `json:"req"`
 }
 
+type ChecksumOption struct {
+	Algorithm string `json:"algorithm"` // "md5" | "sha1" | "sha256"
+	Expected  string `json:"expected"`  // hex-encoded expected hash
+}
+
 // Options for download
 type Options struct {
 	// Download file name
@@ -136,6 +141,8 @@ type Options struct {
 	SelectFiles []int `json:"selectFiles"`
 	// Extra info for specific fetcher
 	Extra any `json:"extra"`
+	// Checksum verification option
+	Checksum *ChecksumOption `json:"checksum,omitempty"`
 }
 
 func (o *Options) InitSelectFiles(fileSize int) {