feat: URL normalisation, strict URLs and the one-hop redirect decision

- Normalize: https, www or bare host, double slashes and index files,
  trailing slash add/remove, optional ASCII lowercasing (defaults change
  nothing but scheme, slashes and index files)
- strict URLs through signpost MatchPath: a path that names a record
  without being its address 301s to the record's address
- resolve runs normalisation, redirects, strict URLs, then SEO; the
  location is the final address, so a visitor makes one hop
- P1 warns when a record's canonical URL redirects

classes/partials.go

@@ -220,24 +220,31 @@ func (s *Service) ruleCallout(ctx context.Context, rules []models.Rule) (Callout
 	return Callout{}, false
 }
 
-// canonicalCallout warns when a canonical on this site resolves to a page
-// served noindex. Outside production every page is noindex, so it says
-// nothing there.
+// canonicalCallout warns about a canonical on this site (D-06): one that
+// redirects (status.canonical_redirected, naming the final address), or
+// one that resolves to a page served noindex (status.canonical_noindex).
+// Outside production every page is noindex, so only the redirect warning
+// applies there.
 func (s *Service) canonicalCallout(ctx context.Context, canonical string) (Callout, bool) {
 	canonical = strings.TrimSpace(canonical)
-	if canonical == "" || s.Staging() {
+	if canonical == "" {
 		return Callout{}, false
 	}
 	target := canonical
 	if u, err := url.Parse(canonical); err == nil && u.IsAbs() {
-		site, err := url.Parse(s.SiteURL())
-		if err != nil || site.Host == "" || !strings.EqualFold(site.Host, u.Host) {
+		if !sameSite(s.SiteURL(), u.Host) {
 			return Callout{}, false
 		}
-		target = u.RequestURI()
+		target = u.String()
 	}
 	res, err := s.Resolver().Resolve(ctx, target)
-	if err != nil || res.SEO == nil || !strings.Contains(res.SEO.Robots, "noindex") {
+	if err != nil {
+		return Callout{}, false
+	}
+	if res.Action == ActionRedirect {
+		return Callout{Title: s.PhraseCtx(ctx, "golem15.seo::lang.status.canonical_redirected", map[string]string{"url": canonical, "target": res.Location})}, true
+	}
+	if s.Staging() || res.SEO == nil || !strings.Contains(res.SEO.Robots, "noindex") {
 		return Callout{}, false
 	}
 	return Callout{Title: s.PhraseCtx(ctx, "golem15.seo::lang.status.canonical_noindex", map[string]string{"url": canonical})}, true