Add mobile nav toggle, responsive admin tables, and menu reordering

- Public site: replace the always-hidden mobile nav with a hamburger
  toggle (index.php, menu.php, main.js, styles.css)
- Admin: render the Menu/Announcements/Users tables as labeled cards
  below ~760px instead of squeezing descriptions into unreadable
  single-word-per-line columns
- Admin menu: replace the manual "Order" number (which allowed
  duplicates and never reflected in real time) with ↑/↓ buttons that
  reorder items and categories immediately and renumber sort_order
  sequentially on every move, self-healing any stale duplicates

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

main.js

@@ -0,0 +1,66 @@
+// Shared public-site behavior: scroll-reveal animations and the mobile
+// nav toggle. Loaded by both index.php and menu.php.
+
+// Reveal-on-scroll
+(() => {
+  if (window.matchMedia('(prefers-reduced-motion: reduce)').matches) return;
+
+  const els = document.querySelectorAll('.reveal');
+  if (!('IntersectionObserver' in window)) {
+    els.forEach((el) => el.classList.add('is-visible'));
+    return;
+  }
+
+  const io = new IntersectionObserver((entries) => {
+    entries.forEach((entry) => {
+      if (entry.isIntersecting) {
+        entry.target.classList.add('is-visible');
+        io.unobserve(entry.target);
+      }
+    });
+  }, { threshold: 0.15 });
+
+  els.forEach((el) => io.observe(el));
+})();
+
+// Mobile nav toggle
+(() => {
+  const toggle = document.getElementById('nav-toggle');
+  const nav = document.getElementById('primary-nav');
+  if (!toggle || !nav) return;
+
+  function closeNav() {
+    nav.classList.remove('is-open');
+    toggle.setAttribute('aria-expanded', 'false');
+  }
+
+  function openNav() {
+    nav.classList.add('is-open');
+    toggle.setAttribute('aria-expanded', 'true');
+  }
+
+  toggle.addEventListener('click', () => {
+    if (nav.classList.contains('is-open')) {
+      closeNav();
+    } else {
+      openNav();
+    }
+  });
+
+  // Close after following a link
+  nav.querySelectorAll('a').forEach((link) => {
+    link.addEventListener('click', closeNav);
+  });
+
+  // Close on Escape
+  window.addEventListener('keydown', (e) => {
+    if (e.key === 'Escape') closeNav();
+  });
+
+  // Close on outside click
+  document.addEventListener('click', (e) => {
+    if (!nav.classList.contains('is-open')) return;
+    if (nav.contains(e.target) || toggle.contains(e.target)) return;
+    closeNav();
+  });
+})();