feat(mix-visualizer): Phase 10 tuning — smooth waveform, bouncy collision, 8 knobs

Smooth the loudness contour (~50 ms envelope at preprocessing + decode-time, plus
smootherstep render reconstruction); retune wax↔waveform collision to bouncy/sub-unity
(no explosion/stuck/jitter); split the bubbles knob into fluid-amount + fluid-viscosity
(cohesion via uniform-only smin/wobble); retune scroll/gravity/heat/width ranges; make
the colour rotation visible and boost OKLab chroma; the controls bar now holds its
layout and hides only its knobs via a Visible parameter.

DeepDrftPublic.Client/Controls/MixZoomMapping.cs

@@ -15,6 +15,27 @@ public static class MixZoomMapping
     /// <summary>Longest span (min zoom). Tunable.</summary>
     public const double MaxVisibleSeconds = 30.0;
 
+    /// <summary>
+    /// Lower edge of the useful zoom band on the underlying fraction axis. Phase 10 retune: the bottom
+    /// 60% of the old knob travel (fraction 0…0.6) was a useless slow/wide window, so the scroll knob's
+    /// full [0,1] travel now maps onto the upper 0.6…1.0 band where every position reads as a useful
+    /// zoom (Daniel: "range below 60% is useless; optimize for the current 60%–110% zoom values" — 110%
+    /// caps at the hard 0.333 s max-zoom anchor, fraction 1.0).
+    /// </summary>
+    public const double ScrollKnobZoomFloor = 0.60;
+
+    /// <summary>
+    /// Maps the scroll-speed knob [0,1] onto the useful zoom band [<see cref="ScrollKnobZoomFloor"/>, 1.0]
+    /// of the underlying fraction axis, then to visible seconds. So knob 0 sits at the slow edge of the
+    /// *useful* range (not the dead slow end), and knob 1 reaches max zoom. Phase 10 scroll retune.
+    /// </summary>
+    public static double ScrollKnobToSeconds(double knob)
+    {
+        knob = Math.Clamp(knob, 0, 1);
+        var fraction = ScrollKnobZoomFloor + (1.0 - ScrollKnobZoomFloor) * knob;
+        return FractionToSeconds(fraction);
+    }
+
     /// <summary>Slider position [0, 1] -> visible seconds. 0 = zoomed out, 1 = zoomed in.</summary>
     public static double FractionToSeconds(double fraction)
     {