build: migrate to bun package manager and enforce with preinstall check

web/package.json

@@ -1,4 +1,11 @@
 {
+  "name": "pacman-web",
+  "description": "A web frontend for the Pac-Man game, including leaderboards and OAuth.",
+  "type": "module",
+  "packageManager": "bun@^1.3.5",
+  "engines": {
+    "bun": ">=1.3.5"
+  },
   "scripts": {
     "preinstall": "npx only-allow bun",
     "dev": "vike dev",
@@ -6,8 +13,6 @@
     "preview": "vike preview",
     "lint": "eslint ."
   },
-  "name": "pacman-web",
-  "description": "A web frontend for the Pac-Man game, including leaderboards and OAuth.",
   "dependencies": {
     "@fontsource/outfit": "^5.2.8",
     "@fontsource/pixelify-sans": "^5.2.7",
@@ -39,6 +44,5 @@
     "typescript": "^5.9.2",
     "typescript-eslint": "^8.42.0",
     "vite": "^7.1.4"
-  },
-  "type": "module"
+  }
 }