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/styles/shared.module.css

@@ -7,13 +7,3 @@
   flex-direction: column;
   overflow: hidden;
 }
-
-.pressable {
-  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.25);
-  transition: transform 80ms ease, box-shadow 80ms ease;
-}
-
-.pressable:active:not(:disabled) {
-  transform: translateY(2px);
-  box-shadow: 0 2px 6px rgba(0, 0, 0, 0.2);
-}