chore: performance baseline for port visualization

[ggfevans]

Parent Epic

Part of #71 (Network Interface Visualization and Connectivity)

Summary

Establish performance baselines before implementing port visualization to measure impact.

Metrics to Capture

• Initial render time (empty rack)
• Render time with 10 devices (no ports)
• Render time with 10 devices × 24 ports = 240 port elements
• Render time with 10 devices × 48 ports = 480 port elements
• Memory usage at each level
• Interaction latency (hover, click response)
• Pan/zoom performance with ports rendered

Test Methodology

1. Use Chrome DevTools Performance panel
2. Measure in production build (not dev mode)
3. Test on mid-range hardware (not just M3 Mac)
4. Document in docs/research/performance-baseline.md

Acceptance Criteria

• Baseline document created with measurements
• Test harness created for repeatable benchmarks
• Performance budget defined (e.g., <16ms render for 60fps)

References

• Spike findings: docs/research/spike-237-network-interface-visualization.md

[ggfevans]

All feedback from CodeRabbit on PR #294 has been addressed in PR #297:

1. ✅ Markdown formatting: Changed **End of Performance Baseline Document** to ## End of Performance Baseline Document for MD036 compliance
2. ✅ Critical boundary check: Fixed generatePlacedDevices() - old check currentU <= rackHeight - 1 prevented valid placements (like 1U at U42). New check properly verifies currentU + deviceType.u_height - 1 <= rackHeight
3. ✅ expectedElements consistency: Added named constants (EMPTY_RACK_ELEMENTS = 384, etc.) and made all scenario calculations consistent with documented SVG element counts