docs: search-index lock-acquisition order and threading model #312

Job	Run time
mypy	21s
Verify prod requirements.txt is sufficient	10s
ruff + pip-audit (windows-latest)	1m 6s
ruff + pip-audit (ubuntu-latest)	25s
Performance benchmarks (gated)	34s
Frontend unit tests (vitest) (ubuntu-latest)	28s
Frontend unit tests (vitest) (windows-latest)	58s
Frontend unit tests (vitest) (macos-latest)	39s
API integration tests + coverage (windows-latest)	56s
ruff + pip-audit (macos-latest)	30s
pytest (windows-latest)	2m 20s
pytest (macos-latest)	38s
pytest (ubuntu-latest)	48s
API integration tests + coverage (ubuntu-latest)	24s
API integration tests + coverage (macos-latest)	21s
	10m 38s

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