Add CI performance benchmarks

[mseminatore]

Issue: Add CI performance benchmarks

Priority: Low
Labels: ci, performance

Description:
GitHub Actions only builds and tests. Add performance regression detection.

Implementation:

• Run gemm_perf, dot_perf, ger_perf in CI
• Store results as artifacts
• Compare against baseline
• Fail CI if performance drops >10%

Acceptance Criteria:

• Add perf benchmarks to CI workflow
• Store baseline performance data
• Implement regression detection
• Report GFlops in CI logs