add prefers-reduced-motion support (#audit-P2)

The transform: scale(.96) animation on button press (and all other
transitions/animations) had no reduced-motion alternative. Added:
@media (prefers-reduced-motion: reduce) { *, *::before, *::after {
  animation-duration: 0s !important;
  animation-iteration-count: 1 !important;
  transition-duration: 0s !important;
}}

Covers btn, btn-icon, snap-slot, transport-btn, switch, file-drop,
loader, and CSS-in-JS elements (preset-chip-s, param-btn, etc.).

public/img/fx_amplifier.svg

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <!-- Generator: Adobe Illustrator 16.0.0, SVG Export Plug-In . SVG Version: 6.00 Build 0)  -->
 <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
-<svg version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px" width="48px"
+<svg fill="#F0EDE6" version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px" width="48px"
 	 height="48px" viewBox="0 0 48 48" enable-background="new 0 0 48 48" xml:space="preserve">
 <g id="Layer_1">
 	<g>