docs: contributor onboarding path and CODEOWNERS #303

Job	Run time
mypy	25s
pytest (windows-latest)	1m 41s
pytest (ubuntu-latest)	50s
API integration tests + coverage (ubuntu-latest)	21s
pytest (macos-latest)	36s
Frontend unit tests (vitest) (ubuntu-latest)	31s
API integration tests + coverage (windows-latest)	1m 5s
Frontend unit tests (vitest) (windows-latest)	54s
Performance benchmarks (gated)	30s
API integration tests + coverage (macos-latest)	22s
Frontend unit tests (vitest) (macos-latest)	31s
ruff + pip-audit (windows-latest)	1m 0s
ruff + pip-audit (ubuntu-latest)	24s
Verify prod requirements.txt is sufficient	6s
ruff + pip-audit (macos-latest)	21s
	9m 37s

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