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/[id]/edit.vue

@@ -114,6 +114,19 @@
             >
           </div>
 
+          <div v-if="piece?.referenceAuto" class="form-control">
+            <label class="label">
+              <span class="label-text">Référence auto</span>
+            </label>
+            <input
+              :value="piece.referenceAuto"
+              type="text"
+              class="input input-bordered input-sm md:input-md bg-base-200"
+              disabled
+              title="Générée automatiquement à partir du type et des champs personnalisés"
+            >
+          </div>
+
           <div class="form-control">
             <label class="label">
               <span class="label-text">Fournisseur</span>