Implement ALTCHA captcha service with challenge generation and solution verification

- Added AltchaService class for managing ALTCHA captcha challenges and solutions.
- Created CaptchaController to handle API requests for generating challenges.
- Introduced CaptchaGuard for validating captcha solutions on public endpoints.
- Developed unit tests for AltchaService to ensure challenge creation and solution verification functionality.
- Implemented integration tests for the Captcha API endpoint and captcha bypass behavior when disabled.
- Added documentation for the Captcha API in the corresponding markdown file.

src/Shared/Captcha/CaptchaController.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace App\Shared\Captcha;
+
+use App\Shared\Controller\BaseController;
+use OpenApi\Attributes as OA;
+use Symfony\Component\HttpFoundation\JsonResponse;
+use Symfony\Component\Routing\Attribute\Route;
+
+#[OA\Tag(name: 'Captcha')]
+class CaptchaController extends BaseController
+{
+    public function __construct(private readonly AltchaService $altcha) {}
+
+    #[OA\Get(
+        path: '/api/v1/altcha/challenge',
+        summary: 'صدور یک challenge امضاشده‌ی ALTCHA برای حل proof-of-work سمت مرورگر',
+        responses: [new OA\Response(response: 200, description: 'ALTCHA challenge object')]
+    )]
+    #[Route('/api/v1/altcha/challenge', methods: ['GET'])]
+    public function challenge(): JsonResponse
+    {
+        return new JsonResponse($this->altcha->createChallenge());
+    }
+}