Add sign toggle button for score entry and email to title screen

Replaces type="number" with type="text" + inputMode="numeric" so iOS
shows the numpad. A +/− toggle button beside each field handles the
sign; it is a no-op when the field is empty. Also adds contact email
below the title on the title screen.

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

src/pages/EnterScores.module.css

@@ -27,6 +27,18 @@
   background: #fff5f5;
 }
 
+.signToggle {
+  width: 2.5rem;
+  height: 2.5rem;
+  border-radius: 50%;
+  border: 2px solid var(--color-parchment-border);
+  background: #fdfaf4;
+  font-size: 1.2rem;
+  font-weight: 600;
+  color: #555;
+  flex-shrink: 0;
+}
+
 .sumLine {
   margin: 0.5rem 0 0;
   text-align: center;