feat(custom-fields) : ajoute endpoint GET /api/custom-fields/names

Retourne la liste plate des noms de champs perso distincts (table
custom_fields), pour alimenter une autocompletion cote frontend.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/Controller/CustomFieldNamesController.php

@@ -0,0 +1,37 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Controller;
+
+use Doctrine\DBAL\Connection;
+use Symfony\Component\HttpFoundation\JsonResponse;
+use Symfony\Component\HttpKernel\Attribute\AsController;
+use Symfony\Component\Routing\Attribute\Route;
+use Symfony\Component\Security\Http\Attribute\IsGranted;
+
+#[AsController]
+final class CustomFieldNamesController
+{
+    public function __construct(private readonly Connection $connection) {}
+
+    #[Route(
+        path: '/api/custom-fields/names',
+        name: 'api_custom_fields_names',
+        methods: ['GET']
+    )]
+    #[IsGranted('ROLE_VIEWER')]
+    public function __invoke(): JsonResponse
+    {
+        $sql = <<<'SQL'
+                SELECT DISTINCT name
+                FROM custom_fields
+                WHERE name IS NOT NULL AND name <> ''
+                ORDER BY name ASC
+            SQL;
+
+        $names = $this->connection->fetchFirstColumn($sql);
+
+        return new JsonResponse($names);
+    }
+}