Add `yarn build` script

package.json

@@ -3,6 +3,7 @@
   "version": "0.0.0",
   "scripts": {
     "dev": "npx webpack-dev-server --config webpack/development.js",
+    "build": "npx webpack --config webpack/development.js",
     "test": "echo \"Error: no test specified\" && exit 1"
   },
   "license": "AGPL-3.0-or-later",