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

site/includes/seo.php

@@ -8,7 +8,7 @@ $ld = [
     'name'     => $ld_gym['name'] !== '' ? $ld_gym['name'] : (($info['name'] ?? '') !== '' ? $info['name'] : 'FitMe 3070'),
     'url'      => gym_url($ld_gym),
     'image'    => base_url(img_compat_rel(($ld_gym['hero_image'] ?? '') !== '' ? $ld_gym['hero_image'] : 'site/assets/img/home.jpg')),
-    'logo'     => base_url('site/assets/img/logos/logo_black.svg'),
+    'logo'     => base_url(img_compat_rel(gym_logo($ld_gym) ?: 'site/assets/img/logos/logo_black.svg')),
 ];
 if (!empty($info['phone'])) $ld['telephone'] = site_tel($info['phone']);
 if (!empty($info['email'])) $ld['email']     = $info['email'];