Figures: several albums per figure, picked on the LED ring

A figure folder that holds album folders instead of audio can play any of them,
up to six, in folder order (depth-first, alphabetical). Each is its own album,
titled "Fuchs - <folder>" and of the figure's kind. Putting the figure down plays
the album it played last, or the first, straight away; another figure placed in
between forgets the position in that album, not the album itself.

Meanwhile the ring offers all of them: one section per album from a fixed palette,
edges shifting towards the neighbours' hue, the selected one bright and wobbling.
The knob moves the selection one section per detent and wraps; pressing plays the
selected album, and left alone for 8 s the picker fades into the figure's colours
and the music carries on. While open, the device hands the knob to the picker
(`capture_knob`): turns do not change the volume and the press is not published to
Home Assistant. A tick per step and a confirm "pling" go with it.

The firmware only draws: one new ring effect, LED_WHEEL_EFFECT_SEGMENT_SELECT (23),
re-sent on every detent with the section to glide from. The look is tunable through
a temporary `general.figure_selection` config section until the right values
become constants.

Every UI sound - the screen's blubb, the parents' timer, the picker - now follows
the music volume with a floor, times a new parent-mode "Effekt-Lautstärke"
(`general.effects_volume`).

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

python-backend/tests/test_effects.py

@@ -15,6 +15,7 @@ from musicmouse.effects import (
     EffectCircularConfig,
     EffectRandomTwoColorInterpolationConfig,
     EffectReverseSwipe,
+    EffectSegmentSelect,
     EffectStaticConfig,
     EffectStaticDetailedConfig,
     EffectSwipeAndChange,
@@ -135,7 +136,54 @@ def test_swipe_and_change_is_the_two_payloads_concatenated() -> None:
         (EffectRandomTwoColorInterpolationConfig(), 35),
         (EffectReverseSwipe(), 12),
         (EffectSwipeAndChange(), 64),
+        (EffectSegmentSelect(colors=(ColorRGBW(0, 0, 0, 0),)), 53),
     ],
 )
 def test_payload_sizes(effect: LedEffect, size: int) -> None:
     assert len(effect.as_bytes()) == size
+
+
+def test_segment_select() -> None:
+    effect = EffectSegmentSelect(
+        colors=(ColorRGBW(1, 0, 0, 0), ColorRGBW(0, 0, 1, 0)),
+        selected=1,
+        previous=0,
+        gap_leds=2,
+        offset_degrees=180.0,
+        direction=-1,
+        dim_factor=0.5,
+        wobble_amplitude=1.5,
+        wobble_period_ms=1000.0,
+        slide_ms=200.0,
+        edge_blend=0.25,
+    )
+    assert effect.as_bytes().hex() == (
+        "02" "01" "00" "02"  # count, selected, previous, gap
+        "ff000000" "0000ff00" + "00000000" * 4  # always six colours on the wire
+        + "00003443"  # offset 180.0
+        "ff"  # direction -1
+        "0000003f"  # dim 0.5
+        "0000c03f"  # wobble 1.5
+        "00007a44"  # period 1000.0
+        "00004843"  # slide 200.0
+        "0000803e"  # edge blend 0.25
+    )
+
+
+def test_segment_select_without_previous_does_not_glide() -> None:
+    effect = EffectSegmentSelect(colors=(ColorRGBW(1, 0, 0, 0),) * 3, selected=2)
+    assert effect.as_bytes()[:3] == bytes([3, 2, 2])
+
+
+def test_segment_select_round_trips() -> None:
+    # Every float exact in float32, as the firmware has them.
+    effect = EffectSegmentSelect(
+        colors=(ColorRGBW(1, 0, 0, 0), ColorRGBW(0, 1, 0, 0)), previous=1, dim_factor=0.25
+    )
+    assert EffectSegmentSelect.from_bytes(effect.as_bytes()) == effect
+
+
+@pytest.mark.parametrize("count", [0, 7])
+def test_segment_select_takes_one_to_six_sections(count: int) -> None:
+    with pytest.raises(ValueError, match="between 1 and 6"):
+        EffectSegmentSelect(colors=(ColorRGBW(1, 0, 0, 0),) * count)