Feature: Recommendation Service

This commit introduces a RecommendationService that is used when indexing products.

The service is utilizing a recommendation rules interface, so many rules can be created and applied during indexing the products

config/catalog.php

@@ -0,0 +1,25 @@
+<?php
+
+use Modules\Core\Catalog\Recommendations\RandomRule;
+use Modules\Core\Catalog\Recommendations\SameCategoryRule;
+
+return [
+    /*
+    |--------------------------------------------------------------------------
+    | Product recommendation rules
+    |--------------------------------------------------------------------------
+    |
+    | Tried in order by Modules\Core\Catalog\Services\RecommendationService —
+    | the first rule that returns at least one product wins. The order here IS
+    | the fallback chain: SameCategoryRule first, then RandomRule as a
+    | last-resort so a product page is never left with zero recommendations
+    | (as long as the store has more than one product). A consuming app can
+    | reorder, add, or remove rules freely — nothing about the chain shape is
+    | hardcoded in the service itself.
+    |
+    */
+    'recommendation_rules' => [
+        SameCategoryRule::class,
+        RandomRule::class,
+    ],
+];