feat(entities) : add description field to Piece and Composant

Add nullable TEXT description column to both pieces and composants
tables with corresponding Doctrine entity mappings, getters/setters
and serialization groups.

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

migrations/Version20260302120000.php

@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+namespace DoctrineMigrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+final class Version20260302120000 extends AbstractMigration
+{
+    public function getDescription(): string
+    {
+        return 'Add description column to pieces and composants tables';
+    }
+
+    public function up(Schema $schema): void
+    {
+        $this->addSql('ALTER TABLE pieces ADD COLUMN IF NOT EXISTS description TEXT DEFAULT NULL');
+        $this->addSql('ALTER TABLE composants ADD COLUMN IF NOT EXISTS description TEXT DEFAULT NULL');
+    }
+
+    public function down(Schema $schema): void
+    {
+        $this->addSql('ALTER TABLE pieces DROP COLUMN IF EXISTS description');
+        $this->addSql('ALTER TABLE composants DROP COLUMN IF EXISTS description');
+    }
+}