fix: correct server port config and seed default settings

- config.ts: rename nixserverPort/nixclientPort to single port, default
  HOST to 127.0.0.1 (installer binds to loopback, Apache proxies)
- index.ts: use config.server.port
- seed.ts: fix wrong default settings (nginx->apache2, bind9->powerdns,
  postfix->exim4, vsftpd->disabled)

server/src/config.ts

@@ -15,9 +15,8 @@ export const config = {
   isDev: optional('NODE_ENV', 'development') === 'development',
 
   server: {
-    host: optional('HOST', '0.0.0.0'),
-    nixserverPort: parseInt(optional('NIXSERVER_PORT', '4000'), 10),
-    nixclientPort: parseInt(optional('NIXCLIENT_PORT', '4001'), 10),
+    host: optional('HOST', '127.0.0.1'),
+    port: parseInt(optional('PORT', '4000'), 10),
   },
 
   db: {