The station position (stationPos) was captured once at ViewModel construction
and never updated when the user clicked on the map or changed the QTH grid.
This caused the radar track line to simply translate instead of being
recalculated from the new position.
Fix:
- Change stationPos and magDeclination from val to var
- Add collectStationPositionChanges() that observes settingsRepo.stationPosition
- On position change: update stationPos, magDeclination, force celestial
recompute, and recalculate the satellite track