feat: domain monitoring (merge plan M2, phase 1)

Port of the domain-intelligence pipeline from the old Beszel fork,
adapted to Dash's SQLite + no-PocketBase architecture:

- internal/domain: RDAP via IANA bootstrap (cached), TCP WHOIS :43
  fallback with multi-format parser, DNS (NS/MX/TXT/CNAME/A/AAAA),
  TLS leaf cert details, ip-api.com geolocation, provider detection
  (DNS/email/hosting/CA). HTML scraping, paid APIs, and exec-based
  whois deliberately dropped.
- API: domains CRUD + synchronous refresh + domain_checks snapshot
  history; refresh runs inside the monitor sweep on interval_h.
- UI: /domains + /domains/:id pages, add/edit dialog, domain board
  widget (favicon + expiry countdown), palette + nav entries,
  domainId picker in the widget dialog.
- Test seam: Server.lookup injects the refresh; domain tests run
  hermetic against a stubbed result.

Verified live: github.com resolves MarkMonitor expiry 2028-10,
Route 53 DNS, GitHub Pages hosting, Sectigo cert with 69d left.

Authored By: TDvorak <[email protected]>

Generated with Devin (https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

apps/backend/internal/api/monitors.go

@@ -450,6 +450,8 @@ func (s *Server) sweep() {
 		AND status != 'down'`); err != nil {
 		s.log.Error("push stale sweep", zap.Error(err))
 	}
+
+	s.sweepDomains()
 }
 
 // runCheck executes one monitor check (with retries) and persists the result.