design: refatorar topbar para visual neutro refinado

- bg-background + border-b (sem cor primária no fundo)
- Links: pill arredondado, hover bg-accent suave, sem underline
- Link ativo: pill bg-primary/10 text-primary
- Trigger aberto: mesma aparência do hover
- Mobile: mesmo padrão de ativo com pill primário

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

components/topbar/app-topbar.tsx

@@ -29,8 +29,8 @@ 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">
-			<div className="w-full max-w-8xl mx-auto px-4 flex items-center gap-3 h-full">
+		<header className="fixed top-0 left-0 right-0 z-50 bg-background border-b h-14 shrink-0 flex items-center">
+			<div className="w-full max-w-8xl mx-auto px-4 flex items-center gap-4 h-full">
 				{/* Logo */}
 				<Link
 					href="/dashboard"