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>

migrations/Version20260312200000.php

@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace DoctrineMigrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+/**
+ * Drop the legacy productIds JSON column from pieces table.
+ * Data has been migrated to the piece_products join table.
+ */
+final class Version20260312200000 extends AbstractMigration
+{
+    public function getDescription(): string
+    {
+        return 'Drop legacy productIds JSON column from pieces table';
+    }
+
+    public function up(Schema $schema): void
+    {
+        $this->addSql('ALTER TABLE pieces DROP COLUMN IF EXISTS productids');
+    }
+
+    public function down(Schema $schema): void
+    {
+        $this->addSql('ALTER TABLE pieces ADD COLUMN productids JSON DEFAULT NULL');
+    }
+}

migrations/Version20260312210000.php

@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace DoctrineMigrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+/**
+ * Drop the legacy structure JSON column from composants table.
+ * Data has been migrated to composant_piece_slots, composant_subcomponent_slots, composant_product_slots tables.
+ */
+final class Version20260312210000 extends AbstractMigration
+{
+    public function getDescription(): string
+    {
+        return 'Drop legacy structure JSON column from composants table';
+    }
+
+    public function up(Schema $schema): void
+    {
+        $this->addSql('ALTER TABLE composants DROP COLUMN IF EXISTS structure');
+    }
+
+    public function down(Schema $schema): void
+    {
+        $this->addSql('ALTER TABLE composants ADD COLUMN structure JSON DEFAULT NULL');
+    }
+}