feat: add landing page templates and registration modal

- Implemented header and hero section in _header.html.twig and _hero_art.html.twig.
- Created a pre-registration modal in _reg_modal.html.twig with form fields and validation.
- Added page scripts for dynamic behavior and interaction in _page_scripts.html.twig.
- Developed landing page structure in landing.html.twig, integrating header, footer, and modal.
- Introduced tests for landing page rendering and registry validation in LandingPageTest.php and LandingRegistryTest.php.

config/packages/twig.yaml

@@ -1,5 +1,9 @@
 twig:
     file_name_pattern: '*.twig'
+    globals:
+        # فوتر مشترک است و در هر دو صفحهٔ اصلی و لندینگ رندر می‌شود؛ global بودن
+        # رجیستری از پاس‌دادن دستی همان متغیر در هر کنترلر جلوگیری می‌کند.
+        landing_pages: '@App\Shared\Landing\LandingRegistry'
 
 when@test:
     twig: