Add a colour wash animation

The frame parks in the middle and the colour changes instead: a gradient
creeps round the colour wheel behind the poster, and the frame's glow
travels with it. Every other animation moves the frame, so the still one
reads as a rest between them rather than as a dead spot.

The wash layer blends with mix-blend-mode: color, which keeps the
poster's luminance and replaces only its hue. soft-light was the first
try and barely shifted the colour at all against a poster already knocked
back to 45% brightness.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Tg15tLAuT6NrCE1ZxKVgDB

config.js

@@ -44,7 +44,17 @@ export const TRAIL_SPACING = 0.6;
 export const TRAIL_LENGTH = 8;
 
 // A still's life, from the moment it lands to fully faded.
-export const TRAIL_FADE_SECONDS = 4;
+export const TRAIL_FADE_SECONDS = 8;
+
+// The colour wash: seconds for one full trip round the colour wheel. Slow
+// enough that the screen never looks like it is flashing — the colour should
+// only be obviously different once you look away and back.
+export const WASH_CYCLE_SECONDS = 90;
+
+// How far apart the two ends of the wash gradient sit on the wheel, in degrees,
+// and how strongly the wash tints the poster underneath it.
+export const WASH_SPREAD = 70;
+export const WASH_STRENGTH = 0.55;
 
 // The frame animations, keyed by the id sent over the socket. The names must
 // match the registry in public/player/motion.js, which supplies the code.
@@ -53,6 +63,7 @@ export const ANIMATIONS = {
   corners: { label: 'Corners' },
   drag: { label: 'Drag & resize' },
   trail: { label: 'Comet trail' },
+  wash: { label: 'Colour wash' },
 };
 
 // Cycle a fresh random animation on every track change. Anything else pins the