feat(catalog): add observable asteroids

[mrosseel]

Summary

• add an MPC Soft00Bright-based minor-planet catalog with stable asteroid numbers and an amateur-oriented magnitude cutoff
• calculate apparent position, H-G magnitude, Earth/Sun distance, opposition or greatest elongation, peak brightness, and topocentric sky motion in arcseconds per hour
• add Nearby, Opposition, Brightest, and Standard asteroid sorting with compact display names and a dedicated asteroid marker
• share atomic background element downloads between comets and asteroids, retaining old data while showing download progress
• migrate saved catalog filters so existing installations gain the asteroid catalog

Stacked directly on the exact sqm-fix/deepchart head from #532 (b1847890). It does not include #528.

Validation

• full unit suite before the direct rebase: 867 passed
• UI integration suite before the direct rebase: 222 passed, 2 skipped
• corrected direct-on-sqm-fix focused suite: 34 passed
• Ruff passed

[mrosseel]

Closed: this was based on the wrong remote branch. The asteroid work is now based directly on origin/deepchart.