rename natus → sky across the codebase — natal chart abstraction is now sky throughout, since chart inputs aren't birthday-gated

Mechanical rename: 5 files (sky-wheel.js, _sky.scss, _sky_overlay.html, SkyWheelSpec.js x2), 24 in-place edits across templates/views/urls/SCSS/JS/tests/CLAUDE.md. URL names epic:natus_save → epic:sky_save (epic namespaced, no clash w. dashboard:sky_save), JS module NatusWheel → SkyWheel, DOM ids id_natus_* → id_sky_*, BEM classes natus-* → sky-*, dashboard sky_natus_data/sky_natus_preview collapsed to sky_data/sky_preview_data. No DB migration needed (User.sky_chart_data + GameEvent.SKY_SAVED already used sky-prefix). 778 ITs + Jasmine green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/static_src/scss/_tray.scss

@@ -258,7 +258,7 @@ $tray-bevel:    0.3rem;  // inner bevel ring; grid must sit inside this
     position: relative;
 
     // Whatever a cell holds (role-card img, sig stage card, future Celtic Cross
-    // / natus wheel / dice) gets a soft drop shadow to lift it off the felt.
+    // / sky wheel / dice) gets a soft drop shadow to lift it off the felt.
     // Applied to the child rather than the cell itself so the dotted grid
     // borders stay shadow-free.
     > * {