[codeforester]

Summary

Addresses #252's governance and continuity scope.

• Add GOVERNANCE.md with current maintainer and independent reviewer responsibilities, review/decision rules, release continuity, reviewer onboarding, health metrics, and succession path.
• Link governance from contributor, documentation, security, and release guidance.
• Refresh the security-support table from 0.4.x to the current 0.5.x line.
• Document the reviewer-training checklist without claiming completion from repository access alone.

The remaining acceptance item is to record completion of the independent reviewer training checklist in the governance/release record.

Validation

• UV_CACHE_DIR=/private/tmp/base-cli-uv-cache uv run --extra dev --extra typer --extra quality ./tests/full_validate.sh --gate contracts
• UV_CACHE_DIR=/private/tmp/base-cli-uv-cache uv run --extra quality ./tests/full_validate.sh --gate style
• git diff --check