Sounds: the Reverb's screen moves (#401)

The sound rings out on the round screen again and again, and the
reflections drift. Only for the look of it.

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

Sounds.md

@@ -1038,6 +1038,11 @@ share of a sound there).
   - A *Sound* draws the peaks of its sound as the rings, each against its loudest. The screen knows
     nothing of the highs there, so the rings are a neutral blue. It says `LOADING` until the sound
     is there, and `NO SOUND` without one.
+  - **It moves** (#401), only for the look of it. The sound rings out again and again in real
+    time: the dot flashes, a thin front runs out over the rings as fast as the tail does and fades
+    as it falls, then a short quiet of 0.8 s. The reflections it passes light up for a moment.
+    The reflections drift slowly round the dot, each at its own pace, sway a little and twinkle,
+    but stay at the time they come. With `wet` at 0 nothing moves.
 - **On the plate**: a button for each type, the sound for *Sound* and four chrome knobs, `Decay`,
   `Damping` and `Pre-delay` under *Space*, `Wet` under *Mix*.
   - The knobs work as the Compressor's do: drag up or down, a double-click resets one, each turn