fix(onboarding): correct Tailwind arbitrary font-family syntax in HouseholdSetupForm

font-['var(--font-display)'] → font-[var(--font-display)] so Fraunces
display font is applied correctly to the h1.

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

frontend/src/lib/onboarding/HouseholdSetupForm.svelte

@@ -38,7 +38,7 @@
 </script>
 
 <form method="POST" novalidate use:enhance onsubmit={handleSubmit}>
-	<h1 class="mb-[8px] font-['var(--font-display)'] text-[24px] font-semibold">Haushalt benennen</h1>
+	<h1 class="mb-[8px] font-[var(--font-display)] text-[24px] font-semibold">Haushalt benennen</h1>
 	<p class="mb-[24px] text-[14px] text-[var(--color-text-muted)]">
 		Gib deinem Haushalt einen Namen, damit du ihn leicht wiederfindest.
 	</p>