Remove dead code

- wire.with_figure: the device uses dataclasses.replace directly.
- DeviceConnected/DeviceDisconnected: emitted, never subscribed to, and a duplicate
  of ConnectionChanged(target="firmware").
- ScreenService.toggle(): never called.
- GET /api/lirc (LircConfigOut, api.lircConfig): no front-end reads it.
- POST /api/volume's delta_percent (api.nudgeVolume): no front-end sends it.
- LibraryCache.shrink_stored_covers: a one-off migration that re-read every cover
  header on every scan. _INDEX_VERSION 7 rebuilds any cache that could still need it.
- Firmware: the MFRC522 library and its unused globals (lib/nfc/rc522.c is the
  driver in use), and mfrc_version.h, a reader test sketch nothing included.

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

python-backend/tests/test_web.py

@@ -288,24 +288,6 @@ async def test_volume_scales_across_the_allowed_range(client: Client, sim: Simul
     assert (await client.get("/api/state")).json()["volume"] == 50
 
 
-async def test_volume_steps_are_relative_to_the_percentage(client: Client, sim: Simulation) -> None:
-    await client.post("/api/volume", json={"percent": 50})
-    await sim.bus.drain()
-    await client.post("/api/volume", json={"delta_percent": 10})
-    await sim.bus.drain()
-
-    assert (await client.get("/api/state")).json()["volume"] == 60
-    assert sim.player.volume == 36
-
-
-async def test_volume_steps_clamp_at_the_ends(client: Client, sim: Simulation) -> None:
-    await client.post("/api/volume", json={"percent": 95})
-    await sim.bus.drain()
-    await client.post("/api/volume", json={"delta_percent": 20})
-    await sim.bus.drain()
-    assert (await client.get("/api/state")).json()["volume"] == 100
-
-
 async def test_remote_steps_move_by_the_volume_increment(client: Client, sim: Simulation) -> None:
     """The +/- buttons take the IR remote's step, in device units, not a percentage."""
     await client.post("/api/volume", json={"percent": 50})