chore: remove internal planning files and adopt proof packages

[saagpatel]

What

Remove internal planning/scratchpad files already present on this branch and add the first proof-package standard implementation.

Why

The repo now needs durable, machine-checkable proof artifacts for cross-repo done-state claims. This branch also continues the existing cleanup lane for public-facing repo hygiene.

Review Of What Was Built

• Adds proof-package.v1 contract documentation.
• Adds a lightweight proof-package validator and tests.
• Converts the PortfolioCommandCenter demo proof into a manifest-backed proof package with explicit producer/subject ownership.

Cleanup Review

This PR includes the earlier branch cleanup removing internal planning/scratchpad files from the public repo surface. The proof-package work is additive and does not remove existing demo images or receipts.

Verification Summary

• python -m pytest tests/test_validate_proof_package.py -q
• .venv/bin/ruff check scripts/validate_proof_package.py tests/test_validate_proof_package.py
• Proof-package validator passed across the cross-repo packages.

Shipped Summary

GithubRepoAuditor now owns the shared proof-package contract and validator, with a real PortfolioCommandCenter demo proof package as the first concrete example.

Next Phase

Keep proof packages refreshed when cross-repo demos, live syncs, dry runs, releases, or runtime burn-ins are used as done-state evidence.

Remaining Roadmap

• Grotto proof package remains local-only until its archived GitHub repository is unarchived.
• Companion proof packages were pushed where remotes allowed.