Add website special-products source setting for storefronts.

Let businesses choose product vs store_item sourcing, defaulting from the store module, and expose it on tenant resolve and store-specials.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/website-api/openapi.json

@@ -169,6 +169,14 @@
                     "faviconUrl": {
                       "type": "string",
                       "nullable": true
+                    },
+                    "specialProductsSource": {
+                      "type": "string",
+                      "enum": [
+                        "product",
+                        "store_item"
+                      ],
+                      "description": "Where homepage special-product carousels read from. Defaults to store_item when the store module is enabled, otherwise product."
                     }
                   }
                 }
@@ -323,7 +331,7 @@
         ],
         "responses": {
           "200": {
-            "description": "{ items: StoreSpecial[] } — each special has id, key, title, items[]"
+            "description": "{ source: product|store_item, items: StoreSpecial[] } — source is the business special-products setting; each special has id, key, title, items[]"
           }
         }
       }