Document the permanent sole-maintainer PR policy

[patschmittdev]

Summary

Update only the current main-policy section in docs/release-checklist.md to match the owner's permanent solo-development policy authorized on 2026-09-12:

• Pull requests remain required, with zero required approving reviews and no last-push approval requirement.
• Explicitly state that GitHub does not enforce two-person review under this policy.
• Retain all seven Actions-bound strict up-to-date CI checks, administrator enforcement, stale-review dismissal when reviews exist, linear history, conversation resolution, and force-push/deletion prohibitions.

The live policy was read back before this documentation change. This PR makes no GitHub settings changes. It starts from main a310af8c3015e78aef059cad5fb3d8596cf4a8eb; the previously reviewed #22 branch remains at 3b1e7d5b07673813cf09b0c94ac12879d6732405.

Trust-boundary impact

None. This is repository development-policy documentation, not a change to external human-key custody, runtime Gold admission, model authority, or retrieval behavior.

Validation

• npm run check passes, including documentation links and style.
• node dist/src/cli/main.js check --root . --audit-clean-room passes with no findings.
• git diff --check passes.
• The diff is limited to one policy section in one Markdown file.
• Merge only through the normal protected path after all required CI passes; no administrator or CI bypass.

Checklist

• Behavior changes include tests that use real temporary files. (No runtime behavior change.)
• Model pathways still cannot write Bronze, knowledge, trust, receipts, reviewed metadata, or indexes.
• No signer, apply, approve, promote command, or --promote flag was added.
• Retrieved content remains reference-only with instruction_authority: none.
• Documentation and compatibility notes match the implementation.
• npm run check passes.
• node dist/src/cli/main.js check --root . --audit-clean-room passes.
• No private key, credential, personal path, or private vault content is included.