docs: adopt doctrine project manifest

[shtse8]

Summary

• Add PROJECT.md and .doctrine/project.json for doctrine project-control-plane adoption.
• Update the existing AGENTS.md with doctrine/project manifest discovery pointers.
• Record Flow canonical-agent-asset boundaries, ADR-29 admission contexts, package release facts, and projection-proof gaps.

Validation

• jq empty .doctrine/project.json
• git diff --check
• python3 /Users/kyle/.doctrine/scripts/project-control-plane-audit.py --local . --fail-on-drift --json -> PRESENT

Scope

Docs/control-plane only. No runtime, CI, deployment, dependency, secret, or infrastructure changes.