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_settings.py

@@ -20,6 +20,7 @@ SETTINGS = {
     "initial_volume": 40,
     "volume_increment": 5,
     "button_leds_brightness": 0.5,
+    "effects_volume": 100,
 }
 
 #: A config file with comments, to prove saving does not flatten them.