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/index.ts

@@ -13,8 +13,8 @@ async function start() {
 
     app = await buildApp()
 
-    await app.listen({ port: config.server.nixserverPort, host: config.server.host })
-    console.log(`[nixpanel] API running on ${config.server.host}:${config.server.nixserverPort}`)
+    await app.listen({ port: config.server.port, host: config.server.host })
+    console.log(`[nixpanel] API running on ${config.server.host}:${config.server.port}`)
 
     startScheduler()