Phase 7D - meteor settings visual pass

- Meteor settings page now reserves a left-side preview panel while retaining the existing controls and pending-world-settings backend.
- Preview uses an eight-frame Earth rotation, orbiting moon, and an eight-direction meteor sprite.
- Meteor is hidden when the event is disabled.
- Earliest-day choices alter the meteor's orbit radius: earlier settings appear closer to Earth, later settings farther away.
- Preview animation is client-render-only and uses system time; it does not add a world/server tick handler.
- Non-meteor settings pages are intentionally unchanged in this pass.
- Base gameplay behavior remains the accepted 0.0.20.2 one-shot meteor implementation.
