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/tests/test_lirc.py

@@ -328,8 +328,8 @@ async def test_the_guide_key_asks_for_the_clock(
     task = await _run_service(sim, _lirc_config(port))
     try:
         await station.wait_connected()
-        await station.send("b7c0000000000000 00 key_epg hauppauge")
-        await station.send("b7c0000000000000 00 key_epg hauppauge")  # still held
+        await station.send("b7c0000000000000 00 key_guide hauppauge")
+        await station.send("b7c0000000000000 00 key_guide hauppauge")  # still held
         await sim.bus.drain()
     finally:
         task.cancel()