Make ISS a selectable city and remove the dedicated ISS view

[aprylewu]

Summary

• Added ISS as a city/location preset that resolves to the station’s current approximate low-Earth-orbit position.
• Removed the dedicated ISS observer/Cupola view, its shortcut, and all related HUD/help text.
• Updated globe markers, hit-testing, setup matching, and export naming so ISS behaves like a normal selectable location while still moving over time.
• Refreshed the README to describe ISS as a selectable observer location instead of a separate mode.

Testing

• cargo fmt --check
• cargo test