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/useMachineDetailUpdates.ts

@@ -73,11 +73,11 @@ export function useMachineDetailUpdates(deps: UseMachineDetailUpdatesDeps) {
   const updateMachineInfo = async () => {
     if (!machine.value) return
     try {
-      const result: any = await updateMachineApi(machine.value.id as string, {
-        name: machineName.value,
-        reference: machineReference.value,
-        siteId: machineSiteId.value || undefined,
-      } as any)
+      const payload: Record<string, unknown> = {}
+      if (machineName.value !== machine.value.name) payload.name = machineName.value
+      if (machineReference.value !== machine.value.reference) payload.reference = machineReference.value
+      if ((machineSiteId.value || undefined) !== ((machine.value.siteId as string) || (machine.value.site as any)?.id || undefined)) payload.siteId = machineSiteId.value || undefined
+      const result: any = await updateMachineApi(machine.value.id as string, payload as any)
       if (result.success) {
         const machinePayload =
           result.data?.machine && typeof result.data.machine === 'object'