test: functional test infrastructure (ApiTestCase + db_test + JWT helpers)

- .env.test points at db_test (doctrine when@test appends _test suffix)
- ApiTestCase: WebTestCase base with createUser/jwtFor/authJson helpers
- InfraSmokeTest: proves boot + DB + JWT auth pipeline works (/health 200,
  unauth /oauth/userinfo 401, JWT-auth userinfo 200)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/Smoke/InfraSmokeTest.php

@@ -0,0 +1,34 @@
+<?php
+
+namespace App\Tests\Smoke;
+
+use App\Tests\ApiTestCase;
+
+/**
+ * Confirms the test infrastructure itself works: app boots, /health serves,
+ * and JWT-authenticated requests reach protected endpoints.
+ */
+class InfraSmokeTest extends ApiTestCase
+{
+    public function testHealthIsPublicAnd200(): void
+    {
+        $this->client->request('GET', '/health');
+        $this->assertSame(200, $this->responseCode());
+    }
+
+    public function testUnauthenticatedApiIs401(): void
+    {
+        $this->client->request('GET', '/oauth/userinfo');
+        $this->assertSame(401, $this->responseCode());
+    }
+
+    public function testJwtAuthReachesUserInfo(): void
+    {
+        $user = $this->createUser(['ROLE_USER']);
+        $body = $this->authJson('GET', '/oauth/userinfo', $user);
+
+        $this->assertSame(200, $this->responseCode());
+        $this->assertTrue($body['success']);
+        $this->assertSame($user->getUuid(), $body['data']['uuid']);
+    }
+}