fix(RichtlinienRuleCard): bg-[#FAF8F1] → bg-parchment design token

Raw hex bypassed the token system and wouldn't remap in dark mode.
Now uses --color-parchment which has a proper dark-mode counterpart.

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

frontend/src/lib/components/RichtlinienRuleCard.svelte

@@ -18,7 +18,7 @@ let { icon, title, body, beispielOutput, beispielLabel = 'Beispiel' }: Props = $
 	<p class="font-serif text-sm leading-relaxed text-ink-2">{body}</p>
 
 	{#if beispielOutput !== undefined}
-		<div class="border-brand-sand mt-4 rounded-sm border bg-[#FAF8F1] px-4 py-3">
+		<div class="border-brand-sand mt-4 rounded-sm border bg-parchment px-4 py-3">
 			<p class="font-sans text-xs font-semibold tracking-wider text-ink-3 uppercase">
 				{beispielLabel}
 			</p>