fix(composant) : replace unique constraint from name to reference validation

Remove DB unique index on composants.name and add Symfony UniqueEntity
validation on reference field with explicit error message.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

migrations/Version20260325214500.php

@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+namespace DoctrineMigrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+final class Version20260325214500 extends AbstractMigration
+{
+    public function getDescription(): string
+    {
+        return 'Remove unique constraint on composants.name (uniqueness on reference is now enforced at application level via UniqueEntity)';
+    }
+
+    public function up(Schema $schema): void
+    {
+        $this->addSql('DROP INDEX IF EXISTS uniq_f95a31995e237e06');
+    }
+
+    public function down(Schema $schema): void
+    {
+        $this->addSql('CREATE UNIQUE INDEX IF NOT EXISTS uniq_f95a31995e237e06 ON composants (name)');
+    }
+}