Add nodemon, nodemon.json and update dev script

Add a nodemon.json config to watch src and public (ext: astro, ts, html), add nodemon as a devDependency, and change the package.json "dev" script to run nodemon --config nodemon.json --exec 'astro build' (replacing the previous "astro dev"). Also remove the preview script.

package.json

@@ -4,9 +4,8 @@
     "node": ">=22.12.0"
   },
   "scripts": {
-    "dev": "astro dev",
+    "dev": "nodemon --config nodemon.json --exec 'astro build'",
     "build": "astro build",
-    "preview": "astro preview",
     "astro": "astro",
     "format": "prettier --write ."
   },
@@ -35,6 +34,7 @@
   },
   "devDependencies": {
     "@iconify-json/mingcute": "^1.2.7",
+    "nodemon": "^3.1.14",
     "prettier": "3.8.1",
     "prettier-plugin-astro": "0.14.1",
     "unplugin-icons": "^23.0.1"