feat: migrate from node to vercel adapter and add vercel config

chore: update package.json dependencies for vercel deployment
fix: add www subdomain to allowed origins in like/dislike API endpoints
chore: add vercel to gitignore

package.json

@@ -35,10 +35,10 @@
     "@astrojs/check": "^0.9.4",
     "@astrojs/markdown-remark": "^6.3.1",
     "@astrojs/mdx": "^4.2.5",
-    "@astrojs/node": "^9.2.1",
     "@astrojs/react": "^4.2.6",
     "@astrojs/rss": "^4.0.11",
     "@astrojs/sitemap": "^3.3.1",
+    "@astrojs/vercel": "^8.1.4",
     "@expressive-code/plugin-collapsible-sections": "^0.41.2",
     "@expressive-code/plugin-line-numbers": "^0.41.2",
     "@fingerprintjs/fingerprintjs": "^4.6.2",
@@ -56,6 +56,7 @@
     "@tailwindcss/vite": "^4.1.4",
     "@types/react": "19.1.2",
     "@types/react-dom": "19.1.2",
+    "@vercel/speed-insights": "^1.2.0",
     "astro": "^5.7.9",
     "astro-expressive-code": "^0.41.2",
     "astro-icon": "^1.1.5",