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

README.md

@@ -39,7 +39,7 @@ autoplay, so the first click is what unlocks audio. One click per session.
 
 ## Animations
 
-The video frame's movement changes with every track. Four animations ship
+The video frame's movement changes with every track. Five animations ship
 today:
 
 - **bounce** — diagonal drift, reflecting off the screen edges.
@@ -55,6 +55,10 @@ today:
   waypoint, and drops a screenshot of itself every frame-width or so. The stills
   stay where they were taken and fade over a few seconds, leaving a comet tail of
   frozen video behind the live one.
+- **wash** — the frame parks in the middle and the colour changes instead: a
+  gradient creeps round the colour wheel behind the poster, taking a minute and
+  a half per lap, and the frame's glow travels with it. The one still animation,
+  which is what makes it worth having between the moving ones.
 
 The queue page's **Animation** buttons pin the player to one of them, which is
 how you look at a single animation without waiting for the cycle to reach it.