feat: add product catalogue and product-aware UI

- introduce product catalogue pages, management view entries and shared product composables\n- wire product selection into component/piece flows and machine skeleton requirements\n- display linked product metadata and documents across machine, component and piece views\n- generalize model type tooling to handle PRODUCT category

app/pages/index.vue

@@ -423,6 +423,12 @@
                   selectedMachineType.pieceRequirements?.length || 0
                 }}</span>
               </div>
+              <div class="flex items-center gap-2">
+                <span class="font-medium">Produits requis :</span>
+                <span class="badge badge-sm">{{
+                  selectedMachineType.productRequirements?.length || 0
+                }}</span>
+              </div>
               <div class="flex items-center gap-2">
                 <span class="font-medium">Catégorie :</span>
                 <span class="badge badge-outline badge-sm">{{