feat(provider): add health-probe contract and supporting value objects

Add getName(), ping(), and probe() to ProviderInterface. Introduce
ProbeTrait to classify HTTP/transport exceptions into typed error codes,
ProviderStatus as the result value object, and ProviderStatusType /
ProviderErrorCode as backing enums.

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

src/Service/ProviderErrorCode.php

@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Service;
+
+enum ProviderErrorCode: string
+{
+    case AuthFailed     = 'auth_failed';
+    case UrlUnreachable = 'url_unreachable';
+    case UserNotFound   = 'user_not_found';
+    case Unknown        = 'unknown';
+}