Fade weather effect in on load and out when toggled…

Details

The seasonal + GPU-snow background layers previously snapped on/off
instantly. Add a 1.1s opacity transition so the weather gently fades in
when the site loads (or when re-enabled) and fades out when the weather
toggle is turned off — the loop keeps running through the fade-out, then
stops and clears once the layer is invisible. The always-on mesh layer is
intentionally excluded, and reduced-motion users get an instant switch.
Verified offline: #season-bg opacity animates 0->1 on load, ->0 on toggle
off, and back to 1 on re-enable; #mesh-bg stays at 1.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Pn8V4h9YWbjYzdSrDiLiVL

Files changed (3)