fix: admin sticky header, pricing rules textarea, hero 3D text shadow

- Admin mobile header: sticky top so it stays visible on scroll
- Pricing rules: auto-expanding textarea instead of single-line input
- Hero text: layered gold+shadow for 3D depth effect

src/app/admin/layout.tsx

@@ -163,7 +163,7 @@ export default function AdminLayout({
       {/* Main content */}
       <div className="flex-1 flex flex-col min-w-0">
         {/* Top bar (mobile) */}
-        <header className="flex items-center gap-3 border-b border-white/10 px-4 py-3 lg:hidden">
+        <header className="sticky top-0 z-30 flex items-center gap-3 border-b border-white/10 bg-neutral-950 px-4 py-3 lg:hidden">
           <button
             onClick={() => setSidebarOpen(true)}
             aria-label="Открыть меню"