enhance(backend): notify new login (#14673)

* wip

* Update CHANGELOG.md

* wip

* fix

* Update index.d.ts

* Update SigninService.ts

* Update MkNotification.vue

packages/backend/src/models/json-schema/notification.ts

@@ -322,6 +322,16 @@ export const packedNotificationSchema = {
 				format: 'id',
 			},
 		},
+	}, {
+		type: 'object',
+		properties: {
+			...baseSchema.properties,
+			type: {
+				type: 'string',
+				optional: false, nullable: false,
+				enum: ['login'],
+			},
+		},
 	}, {
 		type: 'object',
 		properties: {