feat(reference-auto) : display referenceAuto in piece views + formula config in ModelTypeForm

- Piece interface: add referenceAuto field
- piece/[id].vue: read-only display with auto badge
- pieces/[id]/edit.vue: disabled input when referenceAuto is set
- pieces-catalog.vue: new column "Réf. auto"
- PieceItem.vue: badge + detail line for referenceAuto
- ModelTypeForm.vue: formula + required fields config for PIECE category
- modelTypes.ts: add referenceFormula/requiredFieldsForReference to types

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

app/components/PieceItem.vue

@@ -42,6 +42,7 @@
               Rattachée à {{ piece.parentComponentName }}
             </span>
             <span v-if="pieceData.reference" class="badge badge-outline badge-sm">{{ pieceData.reference }}</span>
+            <span v-if="pieceData.referenceAuto" class="badge badge-secondary badge-sm" title="Référence auto">{{ pieceData.referenceAuto }}</span>
             <template v-if="pieceConstructeursDisplay.length">
               <span
                 v-for="constructeur in pieceConstructeursDisplay"
@@ -106,6 +107,10 @@
           pieceData.reference || "Non définie"
         }}</span>
       </div>
+      <div v-if="pieceData.referenceAuto">
+        <span class="font-medium">Référence auto:</span>
+        <span class="ml-2">{{ pieceData.referenceAuto }}</span>
+      </div>
       <div>
         <span class="font-medium">Fournisseur:</span>
         <div v-if="!isEditMode" class="ml-2">
@@ -301,6 +306,7 @@ const emit = defineEmits(['update', 'edit', 'custom-field-update', 'delete'])
 const pieceData = reactive({
   name: props.piece.name || '',
   reference: props.piece.reference || '',
+  referenceAuto: props.piece.referenceAuto || null,
   prix: props.piece.prix || '',
   productId: props.piece.product?.id || props.piece.productId || null,
   quantity: props.piece.quantity ?? 1,