feat(versioning) : add entity versioning frontend with restore flow

- useEntityVersions composable (list, preview, restore API calls)
- EntityVersionList component with auto-refresh after save
- VersionRestoreModal with context-aware messages per entity type
- Integrate into machine, composant, piece, product detail pages
- Add restore action label to historyDisplayUtils
- Show structure slots in composant/piece consultation mode

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

app/pages/piece/[id].vue

@@ -181,17 +181,17 @@
             </div>
           </div>
 
-          <!-- Product requirements (edit mode only) -->
+          <!-- Product requirements -->
           <div
-            v-if="isEditMode && structureProducts.length"
+            v-if="structureProducts.length"
             class="space-y-3 rounded-lg border border-base-200 bg-base-200/40 p-4"
           >
             <header class="space-y-1">
               <h2 class="font-semibold text-base-content">
-                Produit requis par le squelette
+                Produits liés
               </h2>
               <p class="text-xs text-base-content/70">
-                Cette pièce doit rester liée à un produit catalogue répondant aux critères suivants.
+                {{ isEditMode ? 'Cette pièce doit rester liée à un produit catalogue répondant aux critères suivants.' : 'Produits associés à cette pièce via le squelette.' }}
               </p>
             </header>
             <ul class="space-y-2 text-sm text-base-content/80">
@@ -204,7 +204,7 @@
                 <span>{{ description }}</span>
               </li>
             </ul>
-            <div class="grid grid-cols-1 gap-3 md:grid-cols-2">
+            <div v-if="isEditMode" class="grid grid-cols-1 gap-3 md:grid-cols-2">
               <div
                 v-for="entry in productRequirementEntries"
                 :key="entry.key"
@@ -224,6 +224,20 @@
                 />
               </div>
             </div>
+            <div v-else class="grid grid-cols-1 gap-3 md:grid-cols-2">
+              <div
+                v-for="(entry, index) in productRequirementEntries"
+                :key="entry.key"
+                class="form-control"
+              >
+                <label class="label">
+                  <span class="label-text text-xs font-medium">{{ entry.label }}</span>
+                </label>
+                <div class="input input-bordered input-sm md:input-md bg-base-200 flex items-center">
+                  {{ productSelectionLabels[index] || '— Non sélectionné' }}
+                </div>
+              </div>
+            </div>
           </div>
 
           <!-- Skeleton preview (edit mode only) -->
@@ -329,6 +343,14 @@
             :field-labels="historyFieldLabels"
           />
 
+          <EntityVersionList
+            entity-type="piece"
+            :entity-id="String(route.params.id)"
+            :field-labels="historyFieldLabels"
+            :refresh-key="versionRefreshKey"
+            @restored="fetchPiece()"
+          />
+
           <!-- Save buttons (edit mode only) -->
           <div v-if="isEditMode" class="flex flex-col gap-3 md:flex-row md:justify-end">
             <button type="button" class="btn btn-ghost" :class="{ 'btn-disabled': saving }" @click="isEditMode = false">
@@ -369,6 +391,7 @@ const { getConstructeurById } = useConstructeurs()
 const { updateDocument } = useDocuments()
 
 const isEditMode = ref(false)
+const versionRefreshKey = ref(0)
 
 const {
   piece,
@@ -410,12 +433,22 @@ const submitEdition = async () => {
   if (!saving.value) {
     await fetchPiece()
     isEditMode.value = false
+    versionRefreshKey.value++
   }
 }
 
 const editingDocument = ref<any | null>(null)
 const editModalVisible = ref(false)
 
+// Resolve product names for read-only display from piece data
+const productSelectionLabels = computed(() => {
+  if (!piece.value) return []
+  const p = piece.value as any
+  // piece.product contains {id, name} for the legacy single product
+  if (p.product?.name) return [p.product.name]
+  return productSelections.value.map((id: string | null) => id || null)
+})
+
 const visibleCustomFields = computed(() => {
   if (isEditMode.value) return customFieldInputs.value
   return customFieldInputs.value.filter(