Hide play/pause once someone has run out

At a flag the game is over and togglePause is inert anyway — pauseNow
needs RUN, resumeNow needs PAUSE — so the button was there without being
able to do anything. It joins the other two visibility rules in render():
vacant at IDLE or FLAG. Reset stays, being the way out of a finished
game, and the bar comes down to Reset, score and sound.

Checked the whole state machine: shown while running and while paused,
vacant before a game's first tap and at a flag, and pausing and resuming
still work.

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

public_html/index.html

@@ -811,7 +811,9 @@
     var pristine = matchPristine();
     btnSettings.classList.toggle("btn--vacant", !pristine);
     btnReset.classList.toggle("btn--vacant", pristine);            // nothing played to reset
-    btnPlay.classList.toggle("btn--vacant", st.phase === IDLE);    // nothing running to pause
+    // nothing running to pause: before a game's first tap, and after a flag,
+    // where togglePause is inert anyway — the game is over, Reset is the way out
+    btnPlay.classList.toggle("btn--vacant", st.phase === IDLE || st.phase === FLAG);
   }
 
   function loop(){ render(); requestAnimationFrame(loop); }