feat: BLACK HEART DANCE HOUSE landing page

Landing page with Hero, About, Team, Classes, and Contact sections.
Light/dark mode, scroll reveal animations, Yandex Maps, responsive design.
Next.js 16 + Tailwind v4 + TypeScript.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/ui/SectionHeading.tsx

@@ -0,0 +1,15 @@
+interface SectionHeadingProps {
+  children: React.ReactNode;
+  className?: string;
+}
+
+export function SectionHeading({ children, className = "" }: SectionHeadingProps) {
+  return (
+    <h2
+      className={`font-display text-3xl font-bold tracking-tight sm:text-4xl lg:text-5xl ${className}`}
+    >
+      {children}
+      <span className="mt-2 block h-1 w-16 rounded bg-neutral-900 dark:bg-white" />
+    </h2>
+  );
+}