Implement scoresheet page with scoring logic and confirmation dialog

- Add src/game/scoring.ts with computeRunningTotals and isGameOver
- Build ScoreSheet grid: player columns, per-round scores, running totals after round 2+
- Small red "New Game" button in header top-right with full-screen confirmation overlay
- Extend PageFrame with headerAction and overlay props
- Move press animation/shadow from .pressable class to global button selector

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

src/components/PageFrame.tsx

@@ -4,19 +4,23 @@ interface Props {
   title: string
   children: React.ReactNode
   footer?: React.ReactNode
+  headerAction?: React.ReactNode
+  overlay?: React.ReactNode
 }
 
-export default function PageFrame({ title, children, footer }: Props) {
+export default function PageFrame({ title, children, footer, headerAction, overlay }: Props) {
   return (
     <div className={styles.frame}>
       <header className={styles.header}>
         <h1 className={styles.title}>{title}</h1>
         <div className={styles.rule} role="separator" />
+        {headerAction && <div className={styles.headerAction}>{headerAction}</div>}
       </header>
       <div className={styles.content}>
         {children}
       </div>
       {footer && <div className={styles.footer}>{footer}</div>}
+      {overlay && <div className={styles.overlay}>{overlay}</div>}
     </div>
   )
 }