fix(piece) : persist slot quantity on blur and send prix as string

- Save composant piece slot quantity via PATCH on blur
- Pass slotId through hierarchy and selection entries
- Send prix as string (not number) to match backend expectation
- Show quantity in view mode when > 1
- Allow quantity edit for all pieces (not just root-level)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/components/PieceItem.vue

@@ -69,7 +69,7 @@
     <div v-show="!isCollapsed" class="space-y-4">
       <div class="p-4 bg-base-100 border border-base-200 rounded-lg">
         <div class="space-y-2 text-sm">
-      <div v-if="!piece.parentComponentLinkId && isEditMode" class="form-control">
+      <div v-if="isEditMode" class="form-control">
         <label class="label">
           <span class="label-text text-sm">Quantité</span>
         </label>
@@ -82,6 +82,10 @@
           @blur="updatePiece"
         />
       </div>
+      <div v-else-if="displayQuantity > 1">
+        <span class="font-medium">Quantité:</span>
+        <span class="ml-2">{{ displayQuantity }}</span>
+      </div>
       <div>
         <span class="font-medium">Référence:</span>
         <input
@@ -456,7 +460,7 @@ const updatePiece = () => {
   let parsedPrice = null
   if (prixValue !== null && prixValue !== undefined && String(prixValue).trim().length > 0) {
     const numeric = Number(prixValue)
-    if (!Number.isNaN(numeric)) parsedPrice = numeric
+    if (!Number.isNaN(numeric)) parsedPrice = String(numeric)
   }
   const product = selectedProduct.value ? { ...selectedProduct.value } : null
   emit('update', {