feat: add tools/git2muse.py — replay Git commit graph into Muse

Walks main and dev branches oldest-first, extracts each commit's file tree into muse-work/ via git archive, builds the Muse snapshot manifest, and writes CommitRecord objects directly to the Python API preserving original Git author names, emails, and timestamps.

Result: 146 Muse commits on main+dev (143 main, 3 dev-only) mirroring the entire Git history. muse-work/ now holds the current codebase state and 'muse status' correctly diffs against the last replayed commit.

Merge commits are skipped — they carry no unique tree delta; the parent chain on each branch reconstructs the DAG faithfully.