Clock: a "Delphin Uhr" overlay with the school bus and a parents' timer

Einfg on the kiosk keyboard, or Guide (KEY_EPG) on the IR remote, shows a big
analog watch over whatever page is open, built from the Delphin Uhr mockup
without its swimming dolphin. The overlay stays mounted and is only hidden, so it
appears at once. Beside the watch, only while they run:

- The bus: on school days, a silent countdown to `general.clock.bus_time` (07:25)
  that starts `bus_lead_minutes` (60) before. School days skip weekends and the
  school and public holidays of `general.clock.subdivision` (DE-BY), fetched daily
  from openholidaysapi.org and cached under the library cache. A badge on the
  clock says whether there is school today, and why not.
- The dolphin timer, set in parent mode (5/10/15/30 minutes, or until a time).
  It lives in the backend, so a parent's phone can start it for the kiosk. When it
  runs out the kiosk opens the clock at 00:00 and a soft bell chimes on the
  device; it clears after a minute, or at the next key, tap or remote press.

Parent mode is now a way in rather than a page: `?parentMode=1` adds a 🔧 button
next to the ⌨ one, or an "Eltern" tab in the phone's dock, so the URL can stay
bookmarked. The timer comes first there, the device settings below it.

Unmapped IR buttons are logged at debug level, to find out what irserver calls a
new one.

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

python-backend/tests/test_lirc.py

@@ -21,6 +21,7 @@ from musicmouse.events import (
     PlayRequested,
     PlaySeriesLatestRequested,
     PreviousTrackRequested,
+    ToggleClockRequested,
     ToggleScreenRequested,
     VolumeChangeRequested,
 )
@@ -316,6 +317,26 @@ async def test_the_power_button_toggles_the_screen(
     assert len(seen) == 1
 
 
+async def test_the_guide_key_asks_for_the_clock(
+    lircd: tuple[ScriptedLircd, asyncio.base_events.Server], sim: Simulation
+) -> None:
+    station, server = lircd
+    port = server.sockets[0].getsockname()[1]
+    seen: list[Event] = []
+    sim.bus.subscribe(ToggleClockRequested, seen.append)
+
+    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 sim.bus.drain()
+    finally:
+        task.cancel()
+
+    assert [event.source for event in seen] == ["lirc"]
+
+
 async def test_mute_toggles_and_restores(
     lircd: tuple[ScriptedLircd, asyncio.base_events.Server], sim: Simulation
 ) -> None: