refactor(ui): strip all dark: Tailwind classes (single-theme product)

Mechanical sweep of 41 files via `perl -i -pe 's{\s+dark:[\w:/\[\]\.\-]+}{}g'`.
All dark: variants were paired with light-mode counterparts already; no
elements relied on a dark:-only style.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/jury/preferences-banner.tsx

@@ -62,7 +62,7 @@ export function JuryPreferencesBanner() {
   if (isLoading || unconfirmed.length === 0) return null
 
   return (
-    <Card className="border-amber-300 bg-amber-50/50 dark:border-amber-800 dark:bg-amber-950/20">
+    <Card className="border-amber-300 bg-amber-50/50">
       <CardHeader className="pb-3">
         <div className="flex items-center gap-2">
           <Scale className="h-5 w-5 text-amber-600" />