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/app/(jury)/jury/competitions/page.tsx

@@ -54,7 +54,7 @@ export default function JuryAssignmentsPage() {
     <div className="space-y-6">
       <div className="flex items-center justify-between">
         <div>
-          <h1 className="text-2xl font-bold tracking-tight text-brand-blue dark:text-foreground">
+          <h1 className="text-2xl font-bold tracking-tight text-brand-blue">
             My Assignments
           </h1>
           <p className="text-muted-foreground mt-1">