refactor: promote Project Brain Lite 0.3.1

[ruzer]

Summary

• Promotes the deliberately small, deterministic Project Brain Lite core with only brain init, brain sync, and brain doctor.
• Defines and hardens the five-file technical-context contract while preserving RepositoryOwnedContent byte for byte.
• Separates verified observations, heuristic detections, and candidate validation commands; adds compatible role, freshness, and integration warnings.
• Formalizes public result contracts and the Project Memory Hub authority boundary without reintroducing autonomous 0.2.5 capabilities.
• Adds real-process and offline package-consumer verification.

Validation

• npm run check: 140/140 tests and 10 healthy doctor checks.
• npm pack --dry-run: 22 files; @ruzer/project-brain@0.3.1.
• Clean offline tarball install: root and schema imports plus installed brain --help, --version, init, and doctor.
• Repository checkout remains clean after package verification.
• git diff --check clean.

Compatibility and scope

• Node.js 20+.
• Zero npm runtime dependencies.
• Exactly one binary, three commands, and five canonical files.
• doctor remains read-only; init remains non-destructive.
• No agents, swarm, LLM routing, governance, graphs, runtime memory, patch proposals, connectors, databases, plugins, network dependencies, or autonomous execution are reintroduced.

Tracking

Refs #30 and child issues #31-#50.

Release notes

• This PR does not publish to npm.
• After merge and green CI, create tag v0.3.1 and the corresponding GitHub release.
• @ruzer/project-brain is not currently published in the public npm registry; install from the GitHub tag or a local clone.