feat(proxy): add proxy deletion API endpoint

Implement handler for deleting frpc proxies with proper validation and error handling. The endpoint checks user permissions, validates input, removes the proxy configuration from the instance file, and returns appropriate responses.

router.go

@@ -30,6 +30,7 @@ func setupRoutes() {
 	http.HandleFunc("/frpcAct/instanceMgr/modify", ModifyInstanceHandler)
 	http.HandleFunc("/frpcAct/instanceMgr/list", ListInstancesHandler)
 	http.HandleFunc("/frpcAct/proxyMgr/create", CreateProxyHandler)
+	http.HandleFunc("/frpcAct/proxyMgr/delete", DeleteProxyHandler)
 
 	http.HandleFunc("/", NotFoundHandler)