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/pages/pieces-catalog.vue

@@ -69,6 +69,10 @@
             {{ row.piece.reference || '—' }}
           </template>
 
+          <template #cell-referenceAuto="{ row }">
+            {{ row.piece.referenceAuto || '—' }}
+          </template>
+
           <template #cell-description="{ row }">
             <div v-if="row.piece.description" class="group relative">
               <span class="block cursor-help truncate">{{ row.piece.description }}</span>
@@ -174,6 +178,7 @@ const columns = [
   { key: 'preview', label: 'Aperçu', width: 'w-24' },
   { key: 'name', label: 'Nom', sortable: true },
   { key: 'reference', label: 'Référence' },
+  { key: 'referenceAuto', label: 'Réf. auto' },
   { key: 'description', label: 'Description' },
   { key: 'suppliers', label: 'Fournisseurs' },
   { key: 'typePiece', label: 'Type de pièce', filterable: true, filterPlaceholder: 'Filtrer…' },