Adapt for self-hosted deployment on Coolify

- Replace @vercel/postgres with standard pg library
- Add Dockerfile for Next.js standalone build
- Add tsconfig.json, postcss.config.js
- Fix globals.css undefined tailwind utilities
- Force dynamic rendering for DB-dependent pages
- Add .dockerignore

frontend/app/article/[slug]/page.tsx

@@ -1,5 +1,7 @@
-import { sql } from '@vercel/postgres'
+import { sql } from '@/lib/db'
 import { notFound } from 'next/navigation'
+
+export const dynamic = 'force-dynamic'
 import Link from 'next/link'
 import Image from 'next/image'