docs: adopt doctrine project manifest

[shtse8]

Summary

• add repo-local AGENTS.md and PROJECT.md
• add .doctrine/project.json for the forked Rook image boundary and delivery proof
• harden .github/workflows/build.yml so PRs build without pushing GHCR images, and only main push publishes the fixed image tag

Validation

• python3 /Users/kyle/.doctrine/scripts/project-control-plane-audit.py --local /Users/kyle/.codex/worktrees/sylphx-rook-ceph-fork-manifest --repo SylphxAI/rook-ceph-fork --fail-on-drift --json
• python3 /Users/kyle/.doctrine/scripts/project-control-plane-audit.py --repo SylphxAI/rook-ceph-fork --ref codex/project-manifest-adoption --fail-on-drift --json
• python3 -m py_compile patch.py
• git diff --check

Notes

• Workflow guard prevents non-main branch pushes from publishing ghcr.io/sylphxai/rook-ceph-fork:v1.19.3-mon-bypass.