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/enter.html b/enter.html
index 38f8146..170da73 100755
--- a/enter.html
+++ b/enter.html
@@ -216,6 +216,7 @@
 <script>
   Aero.initTheme();
   Aero.spawnBubbles(document.getElementById('bub-stage'), 26);
+  Aero.spawnShards(document.getElementById('bub-stage'), 30, 'shard', 1.5);
   Aero.sparkleCursor();
   Aero.mountThemeSwitcher();
 </script>