feat: internal links widget with counts and suggestions

- E10 golem15-seo-links in the SEO tab after the graph preview (types
  with a body): inbound and outbound counts from the last finished crawl,
  the orphan warning, up to 10 pages to link to (Copy address) and 10
  that could link here
- classes/linkgraph.go builds the report from the crawl's pages and
  links; the crawler's orphan suggestions share NormalText
- GET /_seo/api/v1/links and seo_get_link_suggestions; widget action
  seo_links mapped in AdminOperations
- element bundle rebuilt

controllers/api/links.go

@@ -0,0 +1,33 @@
+package api
+
+import (
+	"context"
+	"net/http"
+
+	"git.golem15.com/golem15/sm-seo-plugin/classes"
+)
+
+// GetLinksInput is the query of GET /_seo/api/v1/links.
+type GetLinksInput struct {
+	URL string `json:"url" query:"url" jsonschema:"the page: a path such as /blog/post or an absolute URL of the site"`
+}
+
+// Links serves GET /_seo/api/v1/links?url= (D-82, UI-SPEC C19): the
+// page's internal links from the last finished crawl, {crawledAt,
+// inbound, outbound, orphan, out [{phrase, title, url}], in [{phrase,
+// title, adminUrl}]}; before the first crawl crawledAt, inbound and
+// outbound are null and the lists empty. A url that is not a path or an
+// http(s) URL is 422.
+func Links(service func() *classes.Service) http.HandlerFunc {
+	return manage(service, func(ctx context.Context, svc *classes.Service, r *http.Request) (int, any, error) {
+		db, err := read(ctx, svc)
+		if err != nil {
+			return 0, nil, err
+		}
+		report, err := svc.LinksOfURL(ctx, db, r.URL.Query().Get("url"))
+		if err != nil {
+			return 0, nil, err
+		}
+		return http.StatusOK, report, nil
+	})
+}