Clock: show it at once and render it cheaply; Guide is KEY_GUIDE

The remote's hauppauge.rem names the Guide button KEY_GUIDE, not lircd's
KEY_EPG, so the remote never toggled the clock.

The overlay is now hidden by opacity rather than display: none, so it is
already laid out and painted when Pos1 or Guide shows it. The drop-shadow
filter on the whole watch is gone (it re-rendered and re-blurred the dial on
every second-hand tick), the hands sit on their own layers, and the bubbles
and countdown cards only exist while the clock is on screen.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

python-backend/config.yml.example

@@ -111,7 +111,7 @@ general:
   # lircd itself is set up on the Pi). Omit the whole section to run without a remote.
   # Play/pause/stop/previous/forward/rewind/volume/mute map to normal music control;
   # number keys 0-9 play whatever the "remote:" section below assigns them; Guide
-  # (KEY_EPG) shows the kiosk's clock. Run with --log-level DEBUG to see the name of a
+  # (KEY_GUIDE) shows the kiosk's clock. Run with --log-level DEBUG to see the name of a
   # button that does nothing.
   lirc:
     host: "musicmouse-pi.local"