Add dynamic DNS: keep A records pointed at the current public IP

For deployments on WAN DHCP, operators can declare A records in the DNS section
that the app updates to this box's current public IP every 4 hours (and
immediately on create).

- utils/public_ip.js: getPublicIp() queries external echo services (ipify +
  fallbacks, configurable) with pure isIPv4/extractIp helpers.
- utils/dns_records.js: pure planARecordUpdate() reconciliation decision.
- models/dns_provider.js: Domain.upsertARecord(name, ip) — provider-agnostic
  upsert via getRecords + deleteRecordById + createRecord (createRecord alone is
  not a reliable cross-provider upsert). Apex ('@') handling added to each
  provider (CloudFlare uses the domain name, Porkbun an empty name, DigitalOcean
  '@') via a new DnsApi.apexName().
- models/dynamic_record.js: DynamicRecord model (deterministic id per host,
  apply()/refreshAll()), registered + ModelPs-wrapped for live UI updates.
- services/dynamic_dns.js + conf: 4h scheduler mirroring host_scheduler.
- routes/dns.js: /dynamic CRUD + /dynamic/ip, gated to domain managers/admins.
- views/dns.ejs: "Dynamic A Records (WAN IP)" card with add form + list.
- test/unit/dynamic_record.test.js: public-IP parsing + reconciliation logic.

Verified end-to-end against a live Porkbun domain (create, idempotent, IP-change,
cleanup) plus unit suite (111 pass).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

nodejs/services/dynamic_dns.js

@@ -0,0 +1,29 @@
+'use strict';
+
+const conf = require('@simpleworkjs/conf');
+const {DynamicRecord} = require('../models').models;
+
+function dynamicDnsService(){
+	/**
+	 * Dynamic DNS Service
+	 *
+	 * Keeps every declared DynamicRecord pointed at this deployment's current
+	 * public (WAN) IP — for sites on WAN DHCP where the IP changes.
+	 *
+	 * Schedule (conf.service.dynamicDns):
+	 * - Initial refresh shortly after start
+	 * - Recurring refresh every 4 hours (14400000ms)
+	 *
+	 * refreshAll resolves the public IP once, then reconciles each record's A
+	 * record via the domain's provider (create/replace only when it drifted).
+	 */
+	setTimeout(DynamicRecord.refreshAll.bind(DynamicRecord), conf.service.dynamicDns.initial);
+	setInterval(DynamicRecord.refreshAll.bind(DynamicRecord), conf.service.dynamicDns.interval);
+
+	console.log('Dynamic DNS service initialized');
+	console.log(`- Public IP refresh: ${conf.service.dynamicDns.initial / 1000}s after start, then every ${conf.service.dynamicDns.interval / 3600000}h`);
+}
+
+if(conf.service.dynamicDns && conf.service.dynamicDns.enabled !== false) dynamicDnsService();
+
+module.exports = {};