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>

src/Controller/MaintenanceController.php

@@ -53,6 +53,6 @@ final class MaintenanceController extends AbstractController
 
     private function flagPath(): string
     {
-        return $this->kernel->getProjectDir() . '/var/maintenance';
+        return $this->kernel->getProjectDir().'/var/maintenance';
     }
 }

src/Entity/Machine.php

@@ -25,7 +25,7 @@ use Symfony\Component\Validator\Constraints as Assert;
 #[ORM\Entity(repositoryClass: MachineRepository::class)]
 #[ORM\Table(name: 'machines')]
 #[ORM\HasLifecycleCallbacks]
-#[UniqueEntity(fields: ['reference'], message: 'Une machine avec cette référence existe déjà.')]
+#[UniqueEntity(fields: ['reference'], message: 'Une machine avec cette référence existe déjà.', ignoreNull: true)]
 #[ApiResource(
     description: 'Machines industrielles rattachées à un site. Chaque machine possède une structure hiérarchique de composants, pièces et produits, ainsi que des champs personnalisés et des documents.',
     operations: [
@@ -150,7 +150,7 @@ class Machine
 
     public function setReference(?string $reference): static
     {
-        $this->reference = $reference;
+        $this->reference = (null !== $reference && '' !== trim($reference)) ? $reference : null;
 
         return $this;
     }

src/EventListener/MaintenanceModeListener.php

@@ -24,14 +24,14 @@ final class MaintenanceModeListener
             return;
         }
 
-        $flagFile = $this->kernel->getProjectDir() . '/var/maintenance';
+        $flagFile = $this->kernel->getProjectDir().'/var/maintenance';
 
         if (!file_exists($flagFile)) {
             return;
         }
 
         $request = $event->getRequest();
-        $path = $request->getPathInfo();
+        $path    = $request->getPathInfo();
 
         // Always allow maintenance status endpoint and session endpoints
         if (str_starts_with($path, '/api/admin/maintenance')