feat(static-pages): navigation integration (insert page link)

Milestone 6 of the Static Pages Module sprint.

- ProjectEditorFacade.addStaticPageNavLink(target, pageId): creates a
  NavigationItemConfig { type: 'staticPage', key: pageId }. This shape was
  already understood end-to-end by the resolvers (StaticPageResolverService/
  FooterResolverService derive label+route from the linked page - see
  footer-resolver.service.ts resolveGroupItem/resolveLegacyItem) - the only
  gap was that the editor UI never exposed a way to create it.
- navigation-section: "Insert page link" control (page picker + button) next
  to both header and footer "Add link". Rows for a static-page link show a
  "Linked to page" indicator instead of the raw label/URL inputs (those
  fields don't apply - the resolver derives them dynamically). labelOf()
  falls back to the page id for the row heading since a static-page link has
  no label of its own.
- i18n: builder.insertPageLink, builder.linkedToPage in interface + en/ru/hy.

Verified (no rebuild needed) that pages already participate in preview(),
exportBootstrap()/importBootstrap(), and draft/publish gating - all flow
through bootstrap.staticPages and the M1-M2 additive fields untouched here.

Gate: tsc --noEmit, npm test (57/57), arch:check, build all green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/i18n/translations.ts

@@ -516,6 +516,8 @@ export interface Translations {
     navigationFooter: string;
     navigationFooterGrouped: string;
     addLink: string;
+    insertPageLink: string;
+    linkedToPage: string;
     removeLink: string;
     linkLabel: string;
     linkUrl: string;