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/translations.ts

@@ -463,6 +463,14 @@ export interface Translations {
     orderLabel: string;
     translationTitle: string;
     htmlPreview: string;
+    seoSection: string;
+    seoTitle: string;
+    seoDescription: string;
+    seoKeywords: string;
+    seoCanonical: string;
+    seoOgTitle: string;
+    seoOgDescription: string;
+    seoOgImage: string;
     visible: string;
     layoutLabel: string;
     columns: string;