infra: add linting and formatting for js projects (#230)

* wip

* wip

* wip

* format

* wip(mobile): lint and format

* cleanup

* nits

* nits

* idiomatic react

* nit

* format all root files

js/mobile/package.json

@@ -9,7 +9,9 @@
     "publish:ios": "eas build --platform ios --auto-submit && echo 'Go to App Store Connect and submit the testflight build for app review. Visit for more information: https://docs.expo.dev/submit/introduction/'",
     "android": "expo run:android",
     "compile": "tsc --noEmit",
-    "lint": "expo lint"
+    "lint": "expo lint",
+    "format": "prettier --write \"src/**/*.{ts,tsx,js,jsx,json,css,md}\" \"*.{ts,tsx,js,cjs,json}\"",
+    "format:check": "prettier --check \"src/**/*.{ts,tsx,js,jsx,json,css,md}\" \"*.{ts,tsx,js,cjs,json}\""
   },
   "packageManager": "[email protected]",
   "dependencies": {
@@ -53,7 +55,11 @@
   },
   "devDependencies": {
     "@types/react": "~19.1.0",
+    "eslint": "^9",
+    "eslint-config-expo": "^56.0.4",
+    "eslint-config-prettier": "^10.1.8",
     "expo-build-properties": "~1.0.10",
+    "prettier": "^3.8.3",
     "tailwindcss": "^3.4.17",
     "typescript": "~5.9.0"
   }