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/index.php

@@ -51,7 +51,7 @@ $hero_img    = $gym['hero_image'] !== '' ? $gym['hero_image'] : 'site/assets/img
 
 <!-- Hero background is inline (no data-setbg) so it paints without waiting for JS;
      the set-bg class is kept for its cover/center styling. -->
-<section id="home" class="hero-section set-bg fade-in" style="background-image:url('<?= htmlspecialchars(base_url($hero_img), ENT_QUOTES) ?>')">
+<section id="home" class="hero-section set-bg fade-in" style="<?= htmlspecialchars(img_css_bg($hero_img), ENT_QUOTES) ?>">
     <div class="container">
         <div class="hero-text">
             <?php /* Eventos a decorrer — destacados no topo do header. Cada um liga
@@ -117,7 +117,7 @@ if ($offer):
 <?php
 // ── Galeria (Instalações) ───────────────────────────────────────────────────────
 $gallery_path  = !empty($gym['gallery_id']) ? 'uploads/gallery/' . (int) $gym['gallery_id'] . '/' : '';
-$gallery_files = ($on('galeria') && $gallery_path !== '') ? preg_grep('/\.(jpe?g|png|gif|webp|jxl)$/i', glob($gallery_path . '*') ?: []) : [];
+$gallery_files = ($on('galeria') && $gallery_path !== '') ? img_list_dir($gallery_path) : [];
 if ($gallery_files && count($gallery_files) > 0):
 $gallery_h2 = 'Conhece as nossas instalações';
 ?>