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/sw.js

@@ -1,5 +1,5 @@
 /* Cache-first: once installed the clock never touches the network again. */
-const CACHE = "bgclock-v16";
+const CACHE = "bgclock-v17";
 const FILES = [
   "./",
   "./index.html",