feat(product): add reusable Product Experience 2.0

Unify product details modules behind config-driven contracts so teams can
extend UX without changing runtime architecture or bootstrap flow.

Keep backward compatibility with existing product payloads by treating new
media/specification/variant/related structures as optional extensions.

Improve conversion and content discoverability with reusable actions,
typed media rendering, grouped specifications, dynamic variants, and
multi-collection related products.

docs/platform/10-product-domain.md

@@ -24,6 +24,10 @@
 - attributes
 - stockStatus
 - rating
+- media
+- specificationGroups
+- variantOptions
+- relatedCollections
 
 ## Product Engagement Models
 - RatingSummary
@@ -41,6 +45,26 @@
   - id, text, author, createdAt
   - isOfficialSeller, isAccepted
 
+## Product Experience 2.0 Optional Contracts
+
+- media: `[{ type, url, thumbnailUrl?, alt?, title?, labels? }]`
+  - type: `image | video | pdf | manual | warranty`
+  - frontend renderer picks viewer by `type`
+- specificationGroups: `[{ key, label?, labels?, attributes: [{ key, value, label?, labels?, unit? }] }]`
+  - supports grouped specifications and translated labels
+- variantOptions: `[{ key, label?, labels?, options: [{ value, label?, labels?, available? }] }]`
+  - supports arbitrary variant groups (`color`, `size`, `storage`, etc.)
+- relatedCollections: `[{ id, title, titles?, products: number[] }]`
+  - supports multiple related collections from backend
+
+## Product Page Config Extensions
+
+`productPage` optional config additions:
+
+- reviews.mode: `pages | load-more`
+- questions.allowSubmission: `boolean`
+- actions: `{ enabled, addToCart, buyNow, wishlist, compare, share, notifyMe }`
+
 ## Строгие правила
 - Цена и валюта должны передаваться как валидная пара.
 - Скрытые товары не участвуют в публичных витринах.
@@ -63,7 +87,35 @@
   "images": [
     { "url": "https://cdn.example.com/items/7812/main.jpg", "isMain": true }
   ],
-  "badges": ["featured", "new"]
+  "badges": ["featured", "new"],
+  "media": [
+    { "type": "image", "url": "https://cdn.example.com/items/7812/main.jpg" },
+    { "type": "video", "url": "https://cdn.example.com/items/7812/demo.mp4" },
+    { "type": "pdf", "url": "https://cdn.example.com/items/7812/spec.pdf" }
+  ],
+  "specificationGroups": [
+    {
+      "key": "display",
+      "labels": { "en": "Display", "ru": "Экран" },
+      "attributes": [
+        { "key": "size", "value": "14", "unit": "inch" },
+        { "key": "resolution", "value": "2880x1800" }
+      ]
+    }
+  ],
+  "variantOptions": [
+    {
+      "key": "storage",
+      "options": [{ "value": "256GB" }, { "value": "512GB" }]
+    }
+  ],
+  "relatedCollections": [
+    {
+      "id": "similar-products",
+      "title": "Похожие товары",
+      "products": [9030, 9031]
+    }
+  ]
 }
 ```
 
@@ -76,3 +128,4 @@
 - Возвращать актуальные цены и доступность.
 - Стабильно поддерживать идентификаторы товаров.
 - Предоставлять медиа и атрибуты в согласованном формате.
+- Поддерживать обратную совместимость: новые поля опциональны, старые payload остаются валидными.