build(website): Dockerfile + production start script for Coolify

Make the marketing site deployable standalone from apps/website (the repo
has no root package.json, so the build must run in this subdir — set Base
Directory to apps/website in Coolify).

- Add a multi-stage Dockerfile (pnpm build -> node .output/server/index.mjs,
  port 3000, NUXT_PUBLIC_SITE_URL default) + .dockerignore.
- Add a "start" script for the Nixpacks path (Nuxt SSR has no default start).
- Guard the bind-mount-only /shared-packages components dir with existsSync
  so standalone builds don't warn on the missing path (the site uses no
  shared component).

apps/website/nuxt.config.ts

@@ -6,6 +6,8 @@
 // the Docker app stack. Locally it runs behind Traefik at dezky.local /
 // www.dezky.local with the same mkcert TLS as the rest of the platform.
 
+import { existsSync } from 'node:fs'
+
 const siteUrl = process.env.NUXT_PUBLIC_SITE_URL
   || (process.env.NODE_ENV === 'production' ? 'https://dezky.eu' : 'http://localhost:3000')
 
@@ -25,7 +27,12 @@ export default defineNuxtConfig({
   // CountrySelect.vue is just <CountrySelect>. Mirrors portal/operator.
   components: [
     '~/components',
-    { path: '/shared-packages/ui/components', pathPrefix: false },
+    // The shared @dezky/ui dir is bind-mounted in the Docker dev stack; include
+    // it only when present so standalone builds (e.g. Coolify) don't warn on
+    // the missing absolute path. The marketing site uses no shared component.
+    ...(existsSync('/shared-packages/ui/components')
+      ? [{ path: '/shared-packages/ui/components', pathPrefix: false }]
+      : []),
   ],
 
   app: {