refactor: desacoplar componentes do top-nav-menu em arquivos separados

- nav-styles.ts: constantes de estilo (linkBase, linkIdle, linkActive, triggerClass)
- simple-nav-link.tsx: link direto com estado ativo
- dropdown-link-list.tsx: lista de itens de dropdown com tipo DropdownLinkItem
- mobile-nav-link.tsx: MobileNavLink e MobileSectionLabel para o Sheet mobile
- top-nav-menu.tsx: apenas TopNavMenu, importa dos arquivos acima

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

components/topbar/app-topbar.tsx

@@ -29,7 +29,7 @@ export function AppTopbar({
 	notificationsSnapshot,
 }: AppTopbarProps) {
 	return (
-		<header className="fixed top-0 left-0 right-0 z-50 bg-card h-14 shrink-0 flex items-center border-b">
+		<header className="fixed top-0 left-0 right-0 z-50 bg-card h-14 shrink-0 flex items-center">
 			<div className="w-full max-w-8xl mx-auto px-4 flex items-center gap-3 h-full">
 				{/* Logo */}
 				<Link