feat(health): make /health report per-provider probe status

Introduce ProviderHealthChecker which probes each configured provider
via AutowireIterator. Wire it into GraphController so /health returns
detailed per-provider status and responds 503 when any provider is
in a degraded state.

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

src/Controller/GraphController.php

@@ -1,8 +1,11 @@
 <?php
 
+declare(strict_types=1);
+
 namespace App\Controller;
 
 use App\Service\ContributionAggregator;
+use App\Service\ProviderHealthChecker;
 use App\Service\SvgRenderer;
 use Psr\Log\LoggerInterface;
 use Symfony\Component\DependencyInjection\Attribute\Autowire;
@@ -13,7 +16,7 @@ use Symfony\Component\Routing\Attribute\Route;
 use Symfony\Contracts\Cache\CacheInterface;
 use Symfony\Contracts\Cache\ItemInterface;
 
-class GraphController
+final class GraphController
 {
     /** @var list<string> */
     private readonly array $allowedHosts;
@@ -23,6 +26,7 @@ class GraphController
         private readonly SvgRenderer $renderer,
         private readonly CacheInterface $cache,
         private readonly LoggerInterface $logger,
+        private readonly ProviderHealthChecker $healthChecker,
         #[Autowire(env: 'ALLOWED_HOSTS')]
         string $allowedHosts = '',
     ) {
@@ -73,8 +77,13 @@ class GraphController
     #[Route('/health', name: 'health', methods: ['GET'])]
     public function health(): Response
     {
-        return new Response('{"status":"ok"}', 200, ['Content-Type' => 'application/json']);
+        $result     = $this->healthChecker->check();
+        $statusCode = $result['status'] === 'degraded' ? 503 : 200;
+
+        return new Response(
+            json_encode($result, JSON_PRETTY_PRINT | JSON_THROW_ON_ERROR),
+            $statusCode,
+            ['Content-Type' => 'application/json'],
+        );
     }
-
-
 }