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

server/index.js

@@ -23,6 +23,9 @@ import {
   TRAIL_SPACING,
   TRAIL_LENGTH,
   TRAIL_FADE_SECONDS,
+  WASH_CYCLE_SECONDS,
+  WASH_SPREAD,
+  WASH_STRENGTH,
   BACKGROUNDS,
   ANIMATIONS,
   AUTO_ANIMATION,
@@ -61,6 +64,9 @@ app.get('/config.js', (_req, res) => {
       `export const TRAIL_SPACING = ${TRAIL_SPACING};\n` +
       `export const TRAIL_LENGTH = ${TRAIL_LENGTH};\n` +
       `export const TRAIL_FADE_SECONDS = ${TRAIL_FADE_SECONDS};\n` +
+      `export const WASH_CYCLE_SECONDS = ${WASH_CYCLE_SECONDS};\n` +
+      `export const WASH_SPREAD = ${WASH_SPREAD};\n` +
+      `export const WASH_STRENGTH = ${WASH_STRENGTH};\n` +
       `export const BACKGROUNDS = ${JSON.stringify(BACKGROUNDS)};\n` +
       `export const ANIMATIONS = ${JSON.stringify(ANIMATIONS)};\n` +
       `export const AUTO_ANIMATION = ${JSON.stringify(AUTO_ANIMATION)};\n`,