Add npm ci to GitHub actions.

Formatting currently being forced to preserve line endings because for
whatever reason that's only causing problems in CI.

client/package.json

@@ -29,6 +29,7 @@
   "scripts": {
     "start": "react-scripts start",
     "build": "react-scripts build",
+    "prepare": "eslint src",
     "test": "react-scripts test",
     "eject": "react-scripts eject",
     "electron": "wait-on tcp:3000 && electron ."
@@ -36,6 +37,9 @@
   "eslintConfig": {
     "extends": "react-app"
   },
+  "prettier": {
+    "endOfLine": "auto"
+  },
   "browserslist": {
     "production": [
       ">0.2%",