Implement enter scores page with per-field and round validation

Each player gets a number input; scores are validated individually
(divisible by 5, ≤ 110) and as a round (must sum to −110). Submit
stays disabled until all constraints pass. A running sum indicator
turns green when the round is valid. Submitting appends the round
to game state and persists it to localStorage.

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

src/pages/EnterScores.module.css

@@ -0,0 +1,40 @@
+.row {
+  display: flex;
+  align-items: center;
+  gap: 0.75rem;
+  margin-bottom: 0.75rem;
+}
+
+.name {
+  flex: 1;
+  font-size: 1.1rem;
+  font-weight: 500;
+}
+
+.scoreInput {
+  width: 6rem;
+  padding: 0.85rem 0.5rem;
+  font-size: 1.1rem;
+  font-family: inherit;
+  text-align: center;
+  border: 1.5px solid var(--color-parchment-border);
+  border-radius: 0.75rem;
+  background: #fdfaf4;
+}
+
+.scoreInputError {
+  border-color: #c0392b;
+  background: #fff5f5;
+}
+
+.sumLine {
+  margin: 0.5rem 0 0;
+  text-align: center;
+  font-size: 0.95rem;
+  color: var(--color-parchment-border);
+}
+
+.sumValid {
+  color: #4a9e6a;
+  font-weight: 600;
+}