feat(tmpl): {{domain_name}} placeholder — materialize on diff/apply, parameterize on snapshot

Adds internal/tmpl with Materialize (template placeholder -> zone name) and
Parameterize (zone name -> placeholder, the inverse used by the
template-from-zone snapshot). service.resolve now materializes the template
against DomainRef.ZoneName before diffing, so one template can be reused
across domains. LoadDomainFull (source query + hand-edited sqlc output, since
sqlc is not installed) now also selects zone_name to populate it.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BwxdSt4reTm7Dj1oxRvpP3

internal/service/service.go

@@ -13,6 +13,7 @@ import (
 	"github.com/vasyakrg/dns-autoresolver/internal/provider"
 	"github.com/vasyakrg/dns-autoresolver/internal/provider/registry"
 	"github.com/vasyakrg/dns-autoresolver/internal/store/dto"
+	"github.com/vasyakrg/dns-autoresolver/internal/tmpl"
 )
 
 // ErrProviderUnavailable marks failures that happened while talking to the
@@ -25,6 +26,7 @@ var ErrProviderUnavailable = errors.New("service: provider unavailable")
 // DomainRef is the minimal data the service needs about a domain.
 type DomainRef struct {
 	ZoneID    string
+	ZoneName  string
 	Provider  string
 	SecretEnc string
 	Template  dto.TemplateDoc
@@ -84,7 +86,7 @@ func (s *DomainService) resolve(ctx context.Context, projectID, domainID uuid.UU
 	if err != nil {
 		return nil, provider.Credentials{}, ref, diff.Changeset{}, err
 	}
-	cs := diff.Diff(ref.Template.ToModel(), actual)
+	cs := diff.Diff(tmpl.Materialize(ref.Template, ref.ZoneName), actual)
 	return p, creds, ref, cs, nil
 }