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

admin_navigation.go

@@ -45,6 +45,7 @@ func (*Plugin) Navigation() []pact.NavigationItem {
 				Permissions: []string{controllers.PermissionManage},
 				Controller:  controllers.PagesControllerID,
 			},
+			// Auto-links, controller golem15.seo.autolinks (UI-SPEC C15).
 			{
 				Code:        "autolinks",
 				Label:       "golem15.seo::lang.nav.autolinks",