fix(pieces) : empêche EntityNotFoundException sur Piece orpheline + UX prévention delete

- Migration FK CASCADE/SET NULL pour toutes les FK vers pieces.id (miroir
  de la fix Composant) + cleanup des orphelins existants avec audit log
- Helper ensurePieceExists() qui catch EntityNotFoundException dans
  MachineStructureController et CustomFieldValueController
- Script SQL standalone scripts/cleanup_orphan_piece_refs.sql pour
  nettoyer la prod sans attendre la migration
- Affiche les machines (avec leur site) utilisant la pièce avant la
  confirmation de suppression

src/Controller/CustomFieldValueController.php

@@ -6,6 +6,7 @@ namespace App\Controller;
 
 use App\Entity\CustomField;
 use App\Entity\CustomFieldValue;
+use App\Entity\Piece;
 use App\Repository\ComposantRepository;
 use App\Repository\CustomFieldRepository;
 use App\Repository\CustomFieldValueRepository;
@@ -15,6 +16,7 @@ use App\Repository\MachineRepository;
 use App\Repository\PieceRepository;
 use App\Repository\ProductRepository;
 use Doctrine\ORM\EntityManagerInterface;
+use Doctrine\ORM\EntityNotFoundException;
 use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
 use Symfony\Component\HttpFoundation\JsonResponse;
 use Symfony\Component\HttpFoundation\Request;
@@ -288,12 +290,31 @@ class CustomFieldValueController extends AbstractController
 
             case 'machinePieceLink':
                 $value->setMachinePieceLink($entity);
-                $value->setPiece($entity->getPiece());
+                $value->setPiece($this->ensurePieceExists($entity->getPiece()));
 
                 break;
         }
     }
 
+    /**
+     * Returns the Piece if its underlying row still exists in DB, otherwise null.
+     * Forces a lazy proxy to initialize via getId() and swallows EntityNotFoundException
+     * so an orphan link to a deleted piece doesn't crash custom-field value writes.
+     */
+    private function ensurePieceExists(?Piece $piece): ?Piece
+    {
+        if (null === $piece) {
+            return null;
+        }
+        try {
+            $piece->getId();
+
+            return $piece;
+        } catch (EntityNotFoundException) {
+            return null;
+        }
+    }
+
     private function normalizeCustomFieldValue(CustomFieldValue $value): array
     {
         $customField = $value->getCustomField();

src/Controller/MachineStructureController.php

@@ -26,6 +26,7 @@ use App\Repository\PieceRepository;
 use App\Repository\ProductRepository;
 use Doctrine\Common\Collections\Collection;
 use Doctrine\ORM\EntityManagerInterface;
+use Doctrine\ORM\EntityNotFoundException;
 use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
 use Symfony\Component\HttpFoundation\JsonResponse;
 use Symfony\Component\HttpFoundation\Request;
@@ -676,7 +677,7 @@ class MachineStructureController extends AbstractController
     private function normalizePieceLinks(array $links): array
     {
         return array_map(function (MachinePieceLink $link): array {
-            $piece      = $link->getPiece();
+            $piece      = $this->ensurePieceExists($link->getPiece());
             $modelType  = $link->getModelType();
             $parentLink = $link->getParentLink();
             $type       = $piece?->getTypePiece();
@@ -704,7 +705,7 @@ class MachineStructureController extends AbstractController
     private function resolvePieceQuantity(MachinePieceLink $link): int
     {
         $parentLink = $link->getParentLink();
-        $piece      = $link->getPiece();
+        $piece      = $this->ensurePieceExists($link->getPiece());
 
         if (!$parentLink || !$piece) {
             return $link->getQuantity();
@@ -716,7 +717,8 @@ class MachineStructureController extends AbstractController
         }
 
         foreach ($composant->getPieceSlots() as $slot) {
-            if ($slot->getSelectedPiece()?->getId() === $piece->getId()) {
+            $selected = $this->ensurePieceExists($slot->getSelectedPiece());
+            if ($selected?->getId() === $piece->getId()) {
                 return $slot->getQuantity();
             }
         }
@@ -771,15 +773,16 @@ class MachineStructureController extends AbstractController
     {
         $pieces = [];
         foreach ($composant->getPieceSlots() as $slot) {
+            $selectedPiece = $this->ensurePieceExists($slot->getSelectedPiece());
             $pieceData = [
                 'slotId'          => $slot->getId(),
                 'typePieceId'     => $slot->getTypePiece()?->getId(),
                 'typePiece'       => $this->normalizeModelType($slot->getTypePiece()),
                 'quantity'        => $slot->getQuantity(),
-                'selectedPieceId' => $slot->getSelectedPiece()?->getId(),
+                'selectedPieceId' => $selectedPiece?->getId(),
             ];
-            if ($slot->getSelectedPiece()) {
-                $pieceData['resolvedPiece'] = $this->normalizePiece($slot->getSelectedPiece());
+            if ($selectedPiece) {
+                $pieceData['resolvedPiece'] = $this->normalizePiece($selectedPiece);
             }
             $pieces[] = $pieceData;
         }
@@ -810,6 +813,25 @@ class MachineStructureController extends AbstractController
         ];
     }
 
+    /**
+     * Returns the Piece if its underlying row still exists in DB, otherwise null.
+     * Forces a lazy proxy to initialize via getId() and swallows EntityNotFoundException
+     * so a stale FK (orphan link to a deleted piece) doesn't crash the whole machine view.
+     */
+    private function ensurePieceExists(?Piece $piece): ?Piece
+    {
+        if (null === $piece) {
+            return null;
+        }
+        try {
+            $piece->getId();
+
+            return $piece;
+        } catch (EntityNotFoundException) {
+            return null;
+        }
+    }
+
     private function normalizePiece(Piece $piece): array
     {
         $type = $piece->getTypePiece();