feat(site): auto-scrolling gallery strip (full-height + 2x2), centre-of-screen hover state, trial link as text under the hero button

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

site/index.php

@@ -77,7 +77,7 @@ $hero_img    = $gym['hero_image'] !== '' ? $gym['hero_image'] : 'site/assets/img
             <h1><?= htmlspecialchars($gym['hero_title'] !== '' ? $gym['hero_title'] : $gym['name']) ?><?php if ($gym['hero_subtitle'] !== ''): ?><br><span><?= htmlspecialchars($gym['hero_subtitle']) ?></span><?php endif; ?></h1>
             <div class="hero-cta-row">
                 <a href="?assunto=insc#contactos" class="site-btn">Inscreve-te Já!</a>
-                <button type="button" class="site-btn sb-ghost" data-bs-toggle="modal" data-bs-target="#trialModal">Marca uma Aula Experimental</button>
+                <button type="button" class="hero-text-link" data-bs-toggle="modal" data-bs-target="#trialModal">Marca uma aula experimental</button>
             </div>
         </div>
     </div>