feat: comprehensive light theme support across entire site

- CSS foundation: theme-aware scrollbars, section glows, glass cards with
  gold shadows, stronger animated borders and glow effects for light mode
- Hero: consistent dark-video treatment for both themes, brighter gold
  gradient text, glowing CTA button
- Gradient text: auto-switch to warm gold tones on light backgrounds via
  html:not(.dark) selector
- Team profile: inverted ambient photo bg with white overlay for light,
  dark text/borders, gold-dark labels for contrast
- All sections: text-neutral-500→600 upgrades for WCAG AA contrast,
  gold shadow accents on cards (About, Pricing, FAQ, DayCard, News)
- Admin: replaced hardcoded #c9a96e with theme tokens, fixed select
  options, array editor borders, booking badges contrast
- Header: white text on transparent hero, dark text after scroll
- UI components: BackToTop, FloatingHearts, ShowcaseLayout tabs,
  SignupModal, NewsModal, GroupCard adapted for light backgrounds
- Updated CLAUDE.md to reflect dual theme support

src/app/admin/_components/CollapsibleSection.tsx

@@ -29,15 +29,15 @@ export function CollapsibleSection({
   const toggle = onToggle ?? (() => setInternalOpen((v) => !v));
 
   return (
-    <div className="rounded-xl border border-white/10 bg-neutral-900/30 overflow-hidden">
+    <div className="rounded-xl border border-neutral-200 bg-neutral-100/50 overflow-hidden dark:border-white/10 dark:bg-neutral-800/50">
       <button
         type="button"
         onClick={toggle}
         aria-expanded={open}
-        className="flex items-center justify-between w-full px-5 py-3.5 text-left cursor-pointer group hover:bg-white/[0.02] transition-colors"
+        className="flex items-center justify-between w-full px-5 py-3.5 text-left cursor-pointer group hover:bg-neutral-100 transition-colors dark:hover:bg-white/[0.02]"
       >
         <div className="flex items-center gap-2">
-          <h3 className="text-sm font-semibold text-neutral-200 group-hover:text-white transition-colors">
+          <h3 className="text-sm font-semibold text-neutral-700 group-hover:text-neutral-900 transition-colors dark:text-neutral-200 dark:group-hover:text-white">
             {title}
           </h3>
           {count !== undefined && (