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/pages/index.vue

@@ -141,13 +141,14 @@
                 </div>
               </div>
               <div class="flex items-center gap-2 shrink-0">
-                <span
-                  class="badge font-bold"
+                <NuxtLink
+                  :to="`/machines?sites=${site.id}`"
+                  class="badge font-bold hover:opacity-80 transition-opacity"
                   :style="site.color ? { backgroundColor: site.color + '30', color: site.color, borderColor: site.color + '50' } : {}"
                   :class="!site.color ? 'badge-primary' : ''"
                 >
-                  {{ site.machines?.length || 0 }}
-                </span>
+                  {{ site.machines?.length || 0 }} machine{{ (site.machines?.length || 0) > 1 ? 's' : '' }}
+                </NuxtLink>
                 <button
                   class="btn btn-ghost btn-xs btn-circle"
                   @click="toggleSiteCollapse(site.id)"