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/utils/public_ip.js

@@ -0,0 +1,69 @@
+'use strict';
+
+// Discover this deployment's current public (WAN) IP by asking an external echo
+// service. Used by the dynamic-DNS feature to keep A records pointed at the box
+// even on WAN DHCP. Pure helpers (isIPv4/extractIp) are unit-tested; getPublicIp
+// does the network calls.
+
+const axios = require('axios');
+const conf = require('@simpleworkjs/conf');
+
+const DEFAULT_SERVICES = [
+	'https://api.ipify.org',
+	'https://icanhazip.com',
+	'https://ifconfig.me/ip',
+];
+
+// Strict dotted-quad IPv4 check (0-255 per octet).
+function isIPv4(str){
+	if(typeof str !== 'string') return false;
+	let m = str.trim().match(/^(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})$/);
+	if(!m) return false;
+	for(let i = 1; i <= 4; i++){
+		if(Number(m[i]) > 255) return false;
+	}
+	return true;
+}
+
+// Pull an IPv4 out of a service response, which may be bare text ("1.2.3.4\n")
+// or JSON ({"ip":"1.2.3.4"}). Returns the IP string or null.
+function extractIp(body){
+	if(body === undefined || body === null) return null;
+
+	if(typeof body === 'object'){
+		let candidate = body.ip || body.address || body.origin;
+		return isIPv4(candidate) ? candidate.trim() : null;
+	}
+
+	let text = String(body).trim();
+	if(isIPv4(text)) return text;
+
+	// Some endpoints wrap the value; try to find the first IPv4 token.
+	let m = text.match(/\b(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\b/);
+	return m && isIPv4(m[1]) ? m[1] : null;
+}
+
+// Try each configured service in order; return the first valid IPv4. Throws if
+// they all fail so the caller can log and skip this cycle.
+async function getPublicIp(){
+	let services = (conf.dynamicDns && conf.dynamicDns.ipServices) || DEFAULT_SERVICES;
+	let lastError;
+
+	for(let url of services){
+		try{
+			let res = await axios.get(url, {timeout: 5000, responseType: 'text'});
+			let ip = extractIp(res.data);
+			if(ip) return ip;
+			lastError = new Error(`No IPv4 in response from ${url}`);
+		}catch(error){
+			lastError = error;
+		}
+	}
+
+	let error = new Error('PublicIpUnavailable');
+	error.name = 'PublicIpUnavailable';
+	error.message = `Could not determine public IP: ${lastError && lastError.message}`;
+	throw error;
+}
+
+module.exports = {isIPv4, extractIp, getPublicIp, DEFAULT_SERVICES};