fix(custom-fields) : context fields display, batch save, hierarchy propagation and UniqueEntity fix

- ComponentItem/PieceItem: DaisyUI divider, emit context-field-update for batch save
- CustomFieldDisplay: support editable/emit-blur/title/show-header props
- MachineComponentsCard/MachinePiecesCard: propagate custom-field-update events
- useMachineDetailCustomFields: pendingContextFieldUpdates + saveAllContextCustomFields
- useMachineDetailData: wire context field save into submitEdition
- useMachineDetailUpdates: only PATCH changed machine fields
- useMachineHierarchy: propagate contextCustomFields/Values from link to nodes
- componentStructure: include machineContextOnly in normalizeStructureForEditor
- Machine entity: convert empty reference to null, ignoreNull on UniqueEntity

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

frontend/app/composables/useMachineHierarchy.ts

@@ -208,6 +208,8 @@ export const buildMachineHierarchyFromLinks = (
       quantity: typeof link.quantity === 'number' ? link.quantity : 1,
       definition: appliedPiece.definition || originalPiece?.definition || {},
       customFields: appliedPiece.customFields || [],
+      contextCustomFields: link.contextCustomFields || [],
+      contextCustomFieldValues: link.contextCustomFieldValues || [],
     }
 
     const resolvedProductId = resolveIdentifier(appliedPiece.productId, (appliedPiece.product as AnyRecord)?.id, link.productId, (link.product as AnyRecord)?.id, originalPiece?.productId, (originalPiece?.product as AnyRecord)?.id)
@@ -335,6 +337,8 @@ export const buildMachineHierarchyFromLinks = (
       parentComposantId: resolveIdentifier(appliedComponent.parentComposantId, link.parentComponentId),
       definition: appliedComponent.definition || originalComponent?.definition || {},
       customFields: appliedComponent.customFields || [],
+      contextCustomFields: link.contextCustomFields || [],
+      contextCustomFieldValues: link.contextCustomFieldValues || [],
       pieces,
       subComponents,
       subcomponents: subComponents,