test: search-index concurrency for rebuild, queries, and lock order (… #328

Job	Run time
Verify prod requirements.txt is sufficient	8s
ruff + pip-audit (ubuntu-latest)	26s
Frontend unit tests (vitest) (macos-latest)	25s
mypy	25s
API integration tests + coverage (macos-latest)	23s
Frontend unit tests (vitest) (ubuntu-latest)	30s
Performance benchmarks (gated)	35s
ruff + pip-audit (windows-latest)	1m 11s
pytest (windows-latest)	1m 41s
Frontend unit tests (vitest) (windows-latest)	1m 2s
pytest (macos-latest)	51s
API integration tests + coverage (windows-latest)	1m 11s
pytest (ubuntu-latest)	51s
API integration tests + coverage (ubuntu-latest)	20s
ruff + pip-audit (macos-latest)	22s
	10m 21s

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