Add DNS monitoring and refresh functionality

Introduce DNS monitoring: add DnsService (comprehensive DNS lookup, crt.sh discovery, Cloudflare detection, IP enrichment) and a new DnsRecord model to persist snapshots, manage diffs, and provide queries/stats. Update DomainController to support a dns_monitoring_enabled flag, refactor WHOIS/DNS refresh logic into performWhoisRefresh/performDnsRefresh, and add endpoints for refreshWhois, refreshDns and refreshAll; send notifications when DNS monitoring is toggled. Add UI templates/tabs for DNS, billing, notifications, overview, SSL and WHOIS and wire DNS data into the domain view; expose cached IP details. Add cron/check_dns.php and migration 027_add_dns_monitoring.sql (and include it in installer migration lists). Other tweaks: safer EmailHelper subject handling, TldRegistry search improvements, domain sorting using an effective status (expiring_soon), Discord channel null-safe fields, settings UI additions (domain_view_template and cron staleness warnings), and route/migration updates. This enables scheduled and manual DNS scans with persistent records and notifications.

app/Services/Channels/DiscordChannel.php

@@ -73,12 +73,12 @@ class DiscordChannel implements NotificationChannelInterface
                 ],
                 [
                     'name' => 'Days Left',
-                    'value' => $data['days_left'],
+                    'value' => (string) ($data['days_left'] ?? 'N/A'),
                     'inline' => true
                 ],
                 [
                     'name' => 'Expiration Date',
-                    'value' => $data['expiration_date'],
+                    'value' => $data['expiration_date'] ?? 'N/A',
                     'inline' => true
                 ]
             ];