Fix light/dark and responsive layout across mobile, tablet, and desktop.

Sync theme toggle with html.dark body styles; Tailwind dark: on nav/footer; tablet uses hamburger until lg; symbol logo in dark mode; mobile menu scroll and contrast; cookie/donate FAB spacing.

Co-authored-by: Cursor <[email protected]>

src/App.tsx

@@ -4336,7 +4336,7 @@ function BackgroundDecor() {
 
 function StickyDonate() {
   return (
-    <div className="fixed bottom-4 right-4 z-50 md:hidden">
+    <div className="fixed bottom-4 left-4 z-40 lg:hidden">
       <a
         href="#/donate"
         className="flex h-14 w-14 items-center justify-center rounded-full bg-gradient-to-br from-primary-500 to-secondary-600 text-white shadow-lg shadow-primary-500/25 transition hover:scale-105"
@@ -4366,8 +4366,8 @@ function CookieBanner() {
   if (!show) return null
 
   return (
-    <div className="fixed bottom-4 left-4 right-4 z-50 card p-4 md:max-w-md md:right-auto" role="dialog" aria-label="Cookie consent">
-      <p className="text-sm">
+    <div className="fixed bottom-20 left-4 right-4 z-40 card p-4 sm:bottom-4 md:max-w-md md:right-auto lg:bottom-4" role="dialog" aria-label="Cookie consent">
+      <p className="text-sm text-neutral-700 dark:text-neutral-200">
         We use cookies to improve your experience. By continuing, you agree to our{' '}
         <a href="#/legal" className="underline focus:outline-none focus-visible:ring-2 focus-visible:ring-primary-500 rounded">cookie policy</a>.
       </p>
@@ -4435,11 +4435,7 @@ function AppContent() {
   }, [])
 
   useEffect(() => {
-    if (darkMode) {
-      document.documentElement.classList.add('dark')
-    } else {
-      document.documentElement.classList.remove('dark')
-    }
+    document.documentElement.classList.toggle('dark', darkMode)
     localStorage.setItem('darkMode', darkMode.toString())
   }, [darkMode])