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/composables/usePieces.ts

@@ -10,6 +10,7 @@ export interface Piece {
   id: string
   name: string
   reference?: string | null
+  referenceAuto?: string | null
   description?: string | null
   typePieceId?: string | null
   typePiece?: { id: string; name?: string } | null