B12: Combat system wiring #150

Summary

Wire the shared combat systems (damage calculation, shield absorption, subsystem damage) into the client for local prediction and visual feedback.

Requirements

• Client-side damage prediction (display damage before server confirms)
• Shield hit detection (determine which shield facing was hit)
• Subsystem health display (read from shared ship state)
• Hook combat events to visual effects (B13-B16)

Acceptance Criteria

• Client predicts damage locally
• Shield facing calculated correctly
• Subsystem health updates displayed
• Combat events trigger visual effects

Depends on: #149 (physics), #144 (ship rendering)
Blocks: #120