test: search-index concurrency for rebuild, queries, and lock order #326

Job	Run time
mypy	25s
pytest (windows-latest)	1m 36s
Frontend unit tests (vitest) (ubuntu-latest)	28s
pytest (macos-latest)	36s
Frontend unit tests (vitest) (macos-latest)	26s
API integration tests + coverage (ubuntu-latest)	35s
API integration tests + coverage (macos-latest)	31s
pytest (ubuntu-latest)	56s
API integration tests + coverage (windows-latest)	55s
Performance benchmarks (gated)	36s
ruff + pip-audit (windows-latest)	1m 8s
Frontend unit tests (vitest) (windows-latest)	1m 22s
ruff + pip-audit (ubuntu-latest)	23s
ruff + pip-audit (macos-latest)	24s
Verify prod requirements.txt is sufficient	6s
	10m 27s

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