B15: Shield hit rendering #153

Summary

Render shield hit effects when a ship takes damage while shields are up. Shield flash shows at the impact point and fades out.

Requirements

• Pre-baked shield mesh (ellipsoid matching ship bounding sphere)
• Hit location calculated from impact direction
• Particle glow at impact point
• Fade-out decay (bright flash → dim → invisible)
• Additive blending
• Different colors per shield strength (blue = full, red = weak)

Acceptance Criteria

• Shield flash appears at correct impact location
• Glow fades out smoothly
• Color varies with shield strength
• Multiple simultaneous shield hits render correctly

Depends on: #150 (combat wiring)
Blocks: #120