feat(site): per-gym SEO texts, event gym selector, hero/navbar polish

- Generated SEO titles/descriptions per gym; gym seo fields override each on its own
- Keywords, author, og:site_name, favicon and JSON-LD logo follow the gym
- CrossFit page 404s before output for gyms without a box
- Events: «Mostrar em» gym selector; event page uses its gym's brand
- Hero event button text colour from the event colour (--ev-on)
- Navbar bottom line stops at the other-gym head (--switch-w)
- Diagonal hero blur mask; remove the trial link

views/admin/events/edit.php

@@ -48,6 +48,7 @@ if ($_SERVER['REQUEST_METHOD'] === 'POST' && isset($_POST['save_event'])) {
         'cta_label'       => trim($_POST['cta_label'] ?? ''),
         'cta_url'         => trim($_POST['cta_url'] ?? ''),
         'show_lead_form'  => isset($_POST['show_lead_form']) ? 1 : 0,
+        'gym_id'          => (int) ($_POST['gym_id'] ?? 0) ?: null,
         'hero_image'      => $item['hero_image'],
     ];