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_library.py

@@ -916,46 +916,3 @@ class TestCoverDownscaling:
             assert thumb.format == "JPEG"
             assert "progressive" not in thumb.info
             assert abs(thumb.width / thumb.height - 2400 / 1800) < 0.02
-
-    def test_thumbnails_are_backfilled_for_covers_stored_without_one(
-        self, tmp_path: Path
-    ) -> None:
-        from PIL import Image
-
-        from musicmouse.library.cache import THUMB_COVER_PX, LibraryCache
-
-        cache = LibraryCache(tmp_path)
-        cache.prepare()
-        cache.cover_path("old").write_bytes(self._jpeg((384, 384)))
-        assert not cache.thumb_path("old").exists()
-
-        assert cache.shrink_stored_covers() == 0  # nothing oversized...
-        with Image.open(cache.thumb_path("old")) as thumb:  # ...but the thumb appeared
-            assert max(thumb.size) == THUMB_COVER_PX
-        # Steady state: the thumbnail is not regenerated, and is not mistaken for a cover.
-        before = cache.thumb_path("old").stat().st_mtime_ns
-        assert cache.shrink_stored_covers() == 0
-        assert cache.thumb_path("old").stat().st_mtime_ns == before
-        assert not cache.thumb_path("old.thumb").exists()
-
-    def test_covers_written_by_an_older_version_are_migrated(self, tmp_path: Path) -> None:
-        """The scanner reuses an unchanged album without re-reading its tags, so a
-        cover stored before the limit existed would otherwise never be rewritten."""
-        from PIL import Image
-
-        from musicmouse.library.cache import MAX_COVER_PX, LibraryCache
-
-        cache = LibraryCache(tmp_path)
-        cache.prepare()
-        stale = cache.cover_path("old")
-        stale.write_bytes(self._jpeg((3000, 3000)))
-        fresh = cache.cover_path("new")
-        fresh.write_bytes(self._jpeg((320, 320)))
-        fresh_before = fresh.read_bytes()
-
-        assert cache.shrink_stored_covers() == 1
-        with Image.open(stale) as image:
-            assert max(image.size) == MAX_COVER_PX
-        assert fresh.read_bytes() == fresh_before
-        # Second pass has nothing left to do - the cheap steady state.
-        assert cache.shrink_stored_covers() == 0