Add nodemon.json for full hot-reload (backend + frontend)

nodemon now watches both server.js and client/src/. On any change,
it rebuilds the React app and restarts Express — so git push makes
both backend AND frontend changes visible on the hot domain.

- dev script simplified to "nodemon" (reads nodemon.json config)
- dev:local added for human developers who want Vite HMR

nodemon.json

@@ -0,0 +1,5 @@
+{
+  "watch": ["server.js", "client/src"],
+  "ext": "js,ts,tsx,jsx,css,json",
+  "exec": "npm run build && node server.js"
+}