Add prepare script to allow npm to build at install time.

package.json

@@ -19,6 +19,7 @@
     "name": "Bruce Harrison"
   },
   "scripts": {
+    "prepare": "npm run build",
     "build": "rollup -c",
     "test": "vitest",
     "lint": "eslint"
@@ -41,4 +42,4 @@
     "vitest": "^1.5.3",
     "vitest-environment-miniflare": "^2.14.2"
   }
-}
+}