feat: links settings and outbound rules in resolve

- migration 202610280003: settings links_new_tab (default on),
  nofollow_domains and sponsored_domains; robots llms_enabled and
  llms_intro (used by the llms.txt commit)
- SEO settings Links tab: the new-tab switch and the two domain lists,
  one domain per line, lowercased, refused with settings.domain_invalid
  naming the line; writable through seo_update_settings
- the resolve answer of an ok page carries outbound {new_tab,
  nofollow_domains, sponsored_domains}; no existing key changes

classes/resolver.go

@@ -57,11 +57,14 @@ type Result struct {
 	Status int    `json:"status"`
 	// Location is the absolute address a redirect answer sends the visitor
 	// to; absent on every other action.
-	Location string            `json:"location,omitempty"`
-	URL      string            `json:"url"`
-	Locale   string            `json:"locale"`
-	Staging  bool              `json:"staging"`
-	SEO      *SEO              `json:"seo"`
+	Location string `json:"location,omitempty"`
+	URL      string `json:"url"`
+	Locale   string `json:"locale"`
+	Staging  bool   `json:"staging"`
+	SEO      *SEO   `json:"seo"`
+	// Outbound is how the layer renders links to other sites (P33-16),
+	// present on ok answers.
+	Outbound *Outbound         `json:"outbound,omitempty"`
 	Sources  map[string]string `json:"-"`
 	// TypeKey and RecordID name the record behind the URL, "" when none.
 	TypeKey  string `json:"-"`
@@ -80,6 +83,35 @@ type SEO struct {
 	Verification []MetaTag  `json:"verification"`
 }
 
+// Outbound holds the settings' Links rules for links to other sites
+// (D-83): open them in a new tab, and the domains (subdomains included)
+// whose links always get nofollow or sponsored.
+type Outbound struct {
+	NewTab           bool     `json:"new_tab"`
+	NofollowDomains  []string `json:"nofollow_domains"`
+	SponsoredDomains []string `json:"sponsored_domains"`
+}
+
+// OutboundOf is the Links rules of the settings.
+func OutboundOf(s models.Settings) *Outbound {
+	return &Outbound{
+		NewTab:           s.LinksNewTab,
+		NofollowDomains:  validDomains(s.NofollowDomains),
+		SponsoredDomains: validDomains(s.SponsoredDomains),
+	}
+}
+
+// validDomains lists the valid domains of a stored list.
+func validDomains(list string) []string {
+	out := []string{}
+	for _, d := range models.DomainLines(list) {
+		if models.ValidDomain(d) {
+			out = append(out, d)
+		}
+	}
+	return out
+}
+
 // OpenGraph holds the og: values.
 type OpenGraph struct {
 	Title       string `json:"title"`
@@ -646,6 +678,7 @@ func (r *Resolver) resolveAt(ctx context.Context, db *gorm.DB, settings models.S
 	}
 
 	res.Action, res.Status, res.Locale, res.SEO = ActionOK, 200, locale, seo
+	res.Outbound = OutboundOf(settings)
 	return res, nil
 }