fix: force single-page flipbook mode on sponsorship page

Set width to 3000 so portrait mode always triggers, showing one slide
at a time instead of two-page spread.

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

components/sponsorship-flipbook.tsx

@@ -44,14 +44,14 @@ export default function SponsorshipFlipbook() {
         {/* @ts-expect-error react-pageflip types are incomplete */}
         <HTMLFlipBook
           ref={bookRef}
-          width={600}
-          height={338}
+          width={3000}
+          height={1688}
           size="stretch"
           minWidth={300}
           maxWidth={1200}
           minHeight={169}
           maxHeight={675}
-          showCover={true}
+          showCover={false}
           mobileScrollSupport={true}
           onFlip={onFlip}
           className="mx-auto"