chrome: add moving shard background + CLAUDE.md

Implements the chrome theme's metallic shard ambient field from the
redesign handoff. Adds spawnShards() to aero.js, shard CSS (clip-path
polygon, chrome gradient, specular streak, shard-rise keyframes) to
aero.css, and wires up calls in index.js and enter.html. Shard field
is hidden by default; shown only when body[data-theme="chrome"].
Also adds prefers-reduced-motion guard for both fields.

Adds CLAUDE.md with architecture overview for future sessions.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/index.js b/index.js
index 28d22e6..06d1f61 100644
--- a/index.js
+++ b/index.js
@@ -2,6 +2,7 @@
   const desk = document.getElementById('desk');
   Aero.makeClouds(document.getElementById('clouds'));
   Aero.spawnBubbles(desk, 24);
+  Aero.spawnShards(desk, 30, 'shard', 1.5);
   Aero.sparkleCursor();
   Aero.mountThemeSwitcher();