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/page.tsx

@@ -1,5 +1,7 @@
-import { sql } from '@vercel/postgres'
+import { sql } from '@/lib/db'
 import ArticleCard from '@/components/ArticleCard'
+
+export const dynamic = 'force-dynamic'
 import TrendingSection from '@/components/TrendingSection'
 import CategoryNav from '@/components/CategoryNav'