feat(images): JPEG XL optimizer with webp/jpg fallback and <picture> serving

img_optimize() decodes .jxl with djxl or Imagick, resizes with GD, re-encodes
with cjxl and writes foto.jxl.webp beside it; skips cleanly without a decoder.
Gallery, hero, navbar logos and JSON-LD serve the JXL with the fallback, and
trash/removal move the fallback with its .jxl.

site/includes/seo.php

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