feat(ui) : clickable entity links, site→machines links, DataTable fixedLayout

- Add NuxtLink on component/piece/product names in machine hierarchy
  (using composantId, pieceId, product.id)
- Make site machine count badges clickable → /machines?sites={id}
- Add opt-in fixedLayout prop and minWidth to DataTable columns

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/app/components/machine/MachineProductsCard.vue

@@ -29,7 +29,14 @@
         >
           <div class="flex items-center justify-between flex-wrap gap-2">
             <p class="font-semibold" :class="product.pendingEntity ? 'text-error' : 'text-base-content'">
-              {{ product.name }}
+              <NuxtLink
+                v-if="!product.pendingEntity && product.id"
+                :to="`/product/${product.id}`"
+                class="hover:underline hover:text-primary transition-colors"
+              >
+                {{ product.name }}
+              </NuxtLink>
+              <span v-else>{{ product.name }}</span>
             </p>
             <div class="flex items-center gap-2">
               <button