fix(player): revert the YouTube modal to its smaller base size

The max-w-6xl bump was a quality lever (bigger pixel box → higher ABR);
the user prefers the smaller max-w-4xl base back. A user-selectable size
preset stays a future item.

frontend/src/components/PlayerModal.tsx

@@ -601,7 +601,7 @@ export default function PlayerModal({
           playlist). Each strip sits just outside the card, spans its full height, and fades out at
           the ends. stopPropagation so a click steps instead of closing. Hidden on narrow screens
           where there's no room beside the card. */}
-      <div className="relative flex w-full max-w-6xl max-h-full">
+      <div className="relative flex w-full max-w-4xl max-h-full">
         {hasQueue && (
           <button
             onClick={(e) => {