- Add showCoverageDegradation() to display before/after GDOP comparison
- Add dismissCoverageDegradation() to clear overlay on node recovery
- Create ground plane cells colored by degradation severity (red/amber/yellow)
- Add legend with before/after statistics and coverage delta
- Export functions to public API for WebSocket integration
Implements plan.md Component 12: before/after coverage overlay
when fleet self-healing fires due to node loss.
Co-Authored-By: Claude <noreply@anthropic.com>
