Add baseline load test metrics to documentation

[AnnabelJoe]

Category: DevOps

Description: Record and publish performance baselines so future optimizations can be measured.

Acceptance Criteria:

• Baseline metrics are documented in docs/PERFORMANCE_BASELINE.md
• Load test commands and expected thresholds are included
• A summary of recent results is maintained

Priority: Medium
Estimated Effort: Small
Dependencies: performance docs
Suggested Labels: devops, performance, documentation