feat(normalization) : drop structure and productIds JSON columns

- Remove Composant.structure property, getter/setter
- Remove Piece.productIds property, setProductIds()
- Update fixtures to remove dropped columns
- Add migrations to drop both columns

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/Entity/Composant.php

@@ -67,10 +67,6 @@ class Composant
     #[Groups(['composant:read'])]
     private ?string $prix = null;
 
-    #[ORM\Column(type: Types::JSON, nullable: true)]
-    #[Groups(['composant:read'])]
-    private ?array $structure = null;
-
     #[ORM\ManyToOne(targetEntity: ModelType::class, inversedBy: 'composants')]
     #[ORM\JoinColumn(name: 'typeComposantId', referencedColumnName: 'id', nullable: true)]
     #[Groups(['composant:read'])]
@@ -203,18 +199,6 @@ class Composant
         return $this;
     }
 
-    public function getStructure(): ?array
-    {
-        return $this->structure;
-    }
-
-    public function setStructure(?array $structure): static
-    {
-        $this->structure = $structure;
-
-        return $this;
-    }
-
     public function getTypeComposant(): ?ModelType
     {
         return $this->typeComposant;