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/conf/base.js

@@ -61,6 +61,20 @@ module.exports = {
 			enabled: true,
 			initial: 30000,
 			interval: 86400000,
+		},
+		dynamicDns:{
+			enabled: true,
+			initial: 15000,      // first refresh 15s after start
+			interval: 14400000,  // then every 4 hours
 		}
 	},
+
+	// Dynamic DNS: services queried (in order) to learn this box's public IP.
+	dynamicDns:{
+		ipServices: [
+			'https://api.ipify.org',
+			'https://icanhazip.com',
+			'https://ifconfig.me/ip',
+		],
+	},
 };

nodejs/conf/development.js

@@ -20,6 +20,11 @@ module.exports = {
 			enabled: true,
 			initial: 5000,
 			interval: 86400000,
+		},
+		dynamicDns:{
+			enabled: true,
+			initial: 8000,
+			interval: 14400000,
 		}
 	},
 };