style(ui): polimento visual — tema, cards, dark mode e landing page

Raio de borda global 0.625rem → 0.7rem; ajustes finos em --card e --border.
DotPattern removido do layout, tela de auth e landing page.
Account-card redesenhado (cores de saldo, tooltip de flags de exclusão).
Budget-card, card-item, calendário (day-cell, event-modal) com layout revisado.
Auth-card-shell simplificado (sem glassmorphism/blob). Landing page com
mainFeatures + extraFeatures em grid único e dark mode nos botões de CTA.
Imagens de preview da landing atualizadas. CSS --data-7..10 removidas.

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

src/shared/components/page-description.tsx

@@ -8,12 +8,12 @@ export default function PageDescription({
 	icon?: React.ReactNode;
 }) {
 	return (
-		<div>
-			<h1 className="text-2xl font-semibold flex items-center gap-1 ">
+		<div className="space-y-2">
+			<h1 className="text-2xl font-semibold flex items-center gap-1">
 				<span className="text-primary">{icon}</span>
 				{title}
 			</h1>
-			<h2 className="text-sm max-w-2xl text-muted-foreground leading-relaxed mt-1.5">
+			<h2 className="text-sm max-w-2xl text-muted-foreground leading-relaxed">
 				{subtitle}
 			</h2>
 		</div>