Save the match every second instead of waiting to be told

A force-quit deep into a turn came back at the clock's last-turn-switch value,
losing the whole interrupted turn. The tell was the delay counter returning at
a full 12: the newest saved state was the one tap() writes, and tap() sets
turnAt and calls saveGame() in the same breath, so it carries held ~ 0.
Restoring it reproduces the moment of the turn switch exactly.

The two triggers meant to save at quit time — visibilitychange and pagehide —
do not fire in Android's WebView. MainActivity's onPause() forwards to
web.onPause() under a comment claiming that is what makes visibilitychange
fire. It isn't: document visibility follows the WebView's view and window
visibility, not that call. The forwarding is still right for stopping timers
and audio, but the saved match should never have depended on it.

This is not new. It has almost certainly been broken since 1.0, and the release
check could not catch it, because for the first 12 seconds of a turn the delay
absorbs everything and render() never touches st.reserve. A clock that has lost
its place is indistinguishable from one that is correctly sitting still, so
every force-quit test that quit soon after a turn change passed. RELEASING.md
now says to let the turn run 40 seconds first, which is the only version of
that check worth running.

So the page stops waiting to be told. A timer writes the match once a second
while a clock is running — a timer rather than a hook in loop(), because
requestAnimationFrame stops when the page is hidden, which is exactly when this
matters. blur joins the listeners too: a different signal, and one that does
fire when the task switcher opens. At most a second can now be lost, which is
well inside the delay nobody is charged for anyway.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

android/app/src/main/java/nl/hansdezwart/bgclock/MainActivity.java

@@ -121,8 +121,15 @@ public class MainActivity extends Activity {
         }
     }
 
-    // forwarded so the page's visibilitychange fires — that is what calls
-    // saveGame() and nudges the audio context back after backgrounding
+    // Forwarded so the WebView stops its timers, animations and audio while the
+    // app is in the background, and picks them up again on return.
+    //
+    // This does NOT drive the page's visibilitychange — an earlier comment here
+    // claimed it did, and the saved match quietly depended on that being true.
+    // Document visibility follows the WebView's view and window visibility, not
+    // this call, so the page can be killed without ever hearing about it. The
+    // page no longer relies on being told: it writes the match to localStorage
+    // once a second while a clock is running.
     @Override
     protected void onPause() {
         super.onPause();