test: add cluster performance benchmark

[huntharo]

Summary

• add a deterministic cluster performance integration benchmark that exercises the real clusterRepository path against a synthetic file-backed SQLite fixture
• run the benchmark in CI and publish a GitHub Actions step summary with the current fixture time, projected openclaw/openclaw cluster duration, and change vs baseline
• fail the perf step when the measured regression exceeds the configured threshold in the committed baseline file

Details

The benchmark uses pre-seeded fake embeddings and does not call GitHub or OpenAI. It stays within the intended short runtime budget by sampling repeated rebuilds of a 512-thread fixture for up to about 10 seconds.

The committed baseline is currently:

• fixture median: 239.1 ms
• projected openclaw/openclaw cluster duration: 10m 0.0s
• regression threshold: +50%

That threshold is intentionally conservative for the first pass because the baseline was bootstrapped locally rather than on a GitHub Actions runner.

Verification

• pnpm --filter @ghcrawl/api-contract build && pnpm --filter @ghcrawl/api-core typecheck
• pnpm --filter @ghcrawl/api-core test
• pnpm --filter @ghcrawl/api-core test:cluster-perf