feat: PWA support with hockey puck icon

Adds full PWA compliance: web app manifest, service worker with
cache-first static / network-first scoreboard strategy, and a
generated hockey puck icon (512, 192, 180, 32px) on the app's
dark navy background. Includes all required meta tags for iOS
standalone mode and a /favicon.ico route.

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

app/static/script.js

@@ -240,4 +240,9 @@ function autoRefresh() {
 window.addEventListener('load', () => {
     autoRefresh();
     setInterval(tickClocks, 1000);
+    if ('serviceWorker' in navigator) {
+        navigator.serviceWorker.register('/sw.js').catch(err => {
+            console.warn('Service worker registration failed:', err);
+        });
+    }
 });