fix: comprehensive UI/UX accessibility and usability improvements

Public site: skip-to-content link, mobile menu focus trap + Escape key,
aria-current on nav, keyboard navigation for carousels/tabs/articles,
ARIA roles (tablist/tab/tabpanel, combobox/listbox, region, dialog),
form labels + aria-describedby, 44px touch targets, semantic HTML
(<time>, <del>), prefers-reduced-motion on Hero scroll hijack,
mobile schedule filters, URL hash sync on scroll for correct refresh.

Admin panel: password toggle aria-label, toast aria-live regions,
SelectField keyboard navigation (Arrow/Enter/Escape), aria-invalid
on validation errors, sidebar hamburger aria-label/expanded,
nav aria-label, ArrayEditor aria-expanded on collapsible items.

src/app/admin/_components/SectionEditor.tsx

@@ -92,7 +92,7 @@ export function SectionEditor<T>({
 
       {/* Fixed toast popup */}
       {(status === "saved" || status === "error") && (
-        <div className={`fixed bottom-4 right-4 z-50 flex items-center gap-2 rounded-lg border px-3 py-2 text-sm shadow-lg animate-in slide-in-from-right ${
+        <div role="status" aria-live="polite" className={`fixed bottom-4 right-4 z-50 flex items-center gap-2 rounded-lg border px-3 py-2 text-sm shadow-lg animate-in slide-in-from-right ${
           status === "saved"
             ? "bg-emerald-950/90 border-emerald-500/30 text-emerald-200"
             : "bg-red-950/90 border-red-500/30 text-red-200"