fix: Use pseudo-element to cover all transparent space above sticky header

Replaces negative margin hack with a ::before that extends upward from
the sticky header to paint bg-background over the main padding gap.

apps/web/src/components/review/ReviewTab.tsx

@@ -325,7 +325,7 @@ export function ReviewTab({ initiativeId }: ReviewTabProps) {
   return (
     <div>
       {/* Header: phase selector + toolbar */}
-      <div ref={headerRef} className="sticky top-0 z-20 -mt-3 pt-3 bg-background">
+      <div ref={headerRef} className="sticky top-0 z-20 before:absolute before:inset-x-0 before:bottom-full before:h-24 before:bg-background">
       <div className="rounded-t-lg border border-border bg-card">
       <ReviewHeader
         phases={reviewablePhases.map((p) => ({ id: p.id, name: p.name, status: p.status }))}