Build a git history rewriter in the sandbox called git_author_fixer.py.

It takes one command-line argument: the path to a git repository. It must
rewrite that repository's ENTIRE history so every commit's author name and
email become exactly:

    AgentLoop <agentloop@local>

Use any git plumbing you like (e.g. `git filter-branch --env-filter` or
`git filter-repo`), but the end state must be:

1. `git log --format='%an <%ae>'` shows ONLY `AgentLoop <agentloop@local>`.
2. The file contents, branch names, and commit topology are unchanged
   (verify with `git log --oneline` — same commit messages and order).
3. The script exits 0 and is safe to run (it must not touch any repo outside
   the given path).

The verifier builds a fresh fixture repo with several commits by different
authors, runs your script against it, and checks the rewritten history.

Test it against the verification oracle before replying DONE.
When the goal is met and verified, reply exactly: DONE.
