[codex] Add deterministic partial-port audit

[Vilin97]

Summary

Adds a deterministic Partial Port Audit workflow for content PRs. For each changed LeanPool project with source.github_repo, the checker clones the upstream GitHub repo, counts non-comment Lean files/LOC, compares that with the imported project files in the PR, and fails with a concrete report when the import is suspiciously incomplete.

The check is intentionally outside the LLM reviewer: it catches the importer-stopped-early failure mode before model judgment, including cases where a headline file is omitted even if total LOC is close.

Validation

• uv run ruff check
• uv run --group test pytest
• Manual smoke checks:
  • flags origin/import/fineqs by LOC ratio
  • flags origin/import/directed-topology-lean-4 for missing Lean4/directed_van_kampen.lean
  • does not flag origin/import/virasoroproject

[Copilot]

Pull request overview

Adds a deterministic Partial Port Audit that catches the "importer stopped early" failure mode for content PRs. For each changed LeanPool project whose source.github_repo is set, the checker clones the upstream repo and compares non-comment Lean LOC and filenames against the imported files; it fails the PR with a concrete report when the import is suspiciously incomplete (LOC ratio below tolerance, or a sufficiently large upstream file with no matching import stem).

Changes:

• New lean_pool.partial_port_audit module implementing diff scan, upstream clone, stem normalization, LOC counting (reuses _strip_lean_comments from quality), and the suspicion heuristic in evaluate_stats.
• New pytest suite covering LOC counting, stem normalization, LOC-ratio gap, missing-large-file detection, ratio-gap fallback to largest unmatched files, and acceptance of near-complete imports.
• New Partial Port Audit GitHub Actions workflow that runs the audit on PRs touching LeanPool/**.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
python/lean_pool/partial_port_audit.py	Core auditor: diff parsing, projects.yml loading, shallow clone, stats, evaluation, CLI.
python/tests/test_partial_port_audit.py	Unit tests for LOC counting, stem matching, and the partial-import heuristics.
.github/workflows/partial-port-audit.yml	PR workflow that syncs Python deps and invokes the audit against the PR base.