feat(admin): product editor auto-slug, SKU helper, one-click SEO fill

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

P0 user feedback: admins did not know what SKU means, had to hand-write slugs, and left SEO empty.

- Name edits now derive the URL slug automatically (supports Cyrillic/Armenian characters); the derivation stops the moment the slug no longer matches the auto value, so a manually edited slug is never overwritten - verified in browser
- SEO title mirrors the name under the same only-while-untouched rule
- SKU field explains itself (what a stock keeping unit is, that any unique text works) and gains a Generate button producing readable codes like WIR-GAM-7K2P from the product name
- SEO tab gains 'Fill from product details': fills only empty title/description/keywords from name and short description, existing text untouched
- New adminProducts keys (slugHint, skuHint, generate, seoGenerate, seoGenerateHint) in en/ru/hy

src/app/i18n/translations.ts

@@ -1545,6 +1545,11 @@ export interface Translations {
     variantsHint: string;
     variants: string;
     archived: string;
+    slugHint: string;
+    skuHint: string;
+    generate: string;
+    seoGenerate: string;
+    seoGenerateHint: string;
     seoExplain: string;
     searchTitle: string;
     searchTitleHint: string;