feat(content-management): expose SEO fields in Static Pages editor

ContentPage.seo (title/description/keywords/canonical/ogTitle/ogDescription/
ogImage) was already modeled and serialized to bootstrap JSON but had no
editable UI. Added updateSeo() to the component and a translated SEO fieldset
using app-form-field/app-input. Added seoSection/seoTitle/seoDescription/
seoKeywords/seoCanonical/seoOgTitle/seoOgDescription/seoOgImage translation
keys to en/ru/hy and the Translations type.

Verified in browser at /edit/static-pages: SEO section renders with
translated labels for all three mock pages.

src/app/i18n/ru.ts

@@ -465,6 +465,14 @@ export const ru: Translations = {
     orderLabel: 'Порядок',
     translationTitle: 'Заголовок перевода',
     htmlPreview: 'HTML',
+    seoSection: 'SEO',
+    seoTitle: 'SEO заголовок',
+    seoDescription: 'SEO описание',
+    seoKeywords: 'Ключевые слова',
+    seoCanonical: 'Canonical URL',
+    seoOgTitle: 'OG заголовок',
+    seoOgDescription: 'OG описание',
+    seoOgImage: 'OG изображение',
     visible: 'Видимость',
     layoutLabel: 'Layout',
     columns: 'Колонки',