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/piece/[id].vue

@@ -113,6 +113,17 @@
             </div>
           </div>
 
+          <!-- Référence auto (read-only, shown only if computed) -->
+          <div v-if="piece.referenceAuto" class="form-control">
+            <label class="label">
+              <span class="label-text">Référence auto</span>
+            </label>
+            <div class="input input-bordered input-sm md:input-md bg-base-200 flex items-center gap-2">
+              <span class="font-mono font-semibold">{{ piece.referenceAuto }}</span>
+              <span class="badge badge-sm badge-ghost">auto</span>
+            </div>
+          </div>
+
           <!-- Référence + Fournisseurs (if value or edit mode) -->
           <div
             v-if="isEditMode || piece.reference || editionForm.constructeurIds.length"