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/next.config.js

@@ -1,5 +1,6 @@
 /** @type {import('next').NextConfig} */
 const nextConfig = {
+  output: 'standalone',
   images: {
     remotePatterns: [
       {
@@ -8,9 +9,6 @@ const nextConfig = {
       },
     ],
   },
-  experimental: {
-    serverActions: true,
-  },
 }
 
 module.exports = nextConfig