feat: proximity-based star radius differentiation

[humzakhan]

Summary

Adds intrinsic stellar size rendering so nearby stars visually reflect physical size differences via the Stefan-Boltzmann relation. Supergiants appear noticeably larger than dwarfs when close, while all stars remain pinpoints at distance for clean map navigation.

Implementation

• Compute radius from luminosity and B-V color index (temperature via Ballesteros formula)
• Log-compress 0.01–1500 R☉ range to [0.3, 3.0] multiplier to prevent extremes
• Apply multiplier only to proximity boost in vertex shader — no effect when distant
• Add EST RADIUS stat to StarInfoPanel showing calculated solar radii

Test Plan

• Build passes with no type errors
• Fly close to known named stars (Betelgeuse, Sirius, etc.) — supergiants appear larger
• Fly far from map origin — all stars render as pinpoints (unchanged behavior)
• Select stars in info panel — EST RADIUS displays correctly formatted values