feat(services): multi-domain, DNS check, maintenance + basic-auth gates (C2)

service_domains table holds the full hostname set; services.domain stays
the derived default and is synced on every domain write. Runtime spec
carries all domains into a multi-Host Traefik rule plus access gates.

- GET|POST /services/:id/domains, DELETE + POST /:domain_id/default
- GET /services/:id/domains/check — DNS preflight vs public_ip/base_url
  (ok | wrong-target | pending), stamps last_checked_at
- maintenance_mode → Traefik redirectregex to /api/v1/maintenance
  (base_url/BASE_URL setting; falls back to noop@internal offline)
- basic_auth [{username,password}] → bcrypt htpasswd on the label;
  responses return usernames only
- First domain auto-defaults; domain="" via PUT clears all domains
- CLI: services domains list|add|remove|default|check, update
  --maintenance/--basic-auth; MCP: 5 domain tools + update args
- Settings UI: Domains card (CRUD + DNS check badges) + Access card
- Fixes latent C1 bug: PUT without volumes 500'd — nil []byte sent as
  bytea, not NULL; COALESCE needs untyped nil + ::jsonb cast

Verified live: domain CRUD + default sync, pending/wrong-target checks,
bcrypt htpasswd and both middlewares on the deployed container's labels.

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

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

app/backend/internal/api/runtime.go

@@ -54,6 +54,11 @@ func serviceRuntimeSpec(db *database.DB, service Service) (deployment.RuntimeSpe
 	spec.NanoCPUs = parseCPULimit(service.CPU)
 	spec.MemoryBytes = parseMemoryLimit(service.Memory)
 	spec.Volumes = loadServiceVolumes(db, service.ID)
+	spec.Domains = serviceDomainNames(db, service.ID, service.Domain)
+	spec.Maintenance, spec.BasicAuthUsers = serviceAccess(db, service.ID)
+	if spec.Maintenance {
+		spec.MaintenanceURL = maintenanceURL(db)
+	}
 	if spec.Port > 0 {
 		env["PORT"] = strconv.Itoa(service.Port)
 	}