feat(tools): add scoped path filtering to git_log

[Preciousuche]

Description

closes #623

### Summary
Adds optional path filtering to the built-in `git_log` tool in `src/agentos/tools/builtin/git.py`.

### Problem
Previously, `git_log` only supported `count` and `workdir`. When an agent investigated changes to a specific file or directory, it had to retrieve the top `N` commits across the entire repository. This consumed unnecessary context tokens and missed older commits that touched the target file.

### Changes
- Added optional `path: str | None = None` parameter to `git_log()`.
- Validated `path` using `_reject_foreign_git_path(path)` to prevent directory traversal and foreign Windows path injections.
- Added `_git_log_argv` helper to derive clean sandboxed arguments (`git log --max-count=N -- path`).
- Added unit tests in `tests/test_tools/test_git_workdir_policy.py` and path-scoping integration tests in `tests/test_security/test_git_output_redaction.py`.

### Verification
- `uv run pytest tests/test_tools/test_git_workdir_policy.py` (7 passed)
- `uv run pytest tests/test_security/test_git_output_redaction.py` (23 passed)
- `ruff check`, `ruff format`, and `mypy` all passed with 0 errors.

[andreapn]

Closing along with #623, which I closed as wontfix. git_log returns correct results today; the missing path costs some extra tokens, not correctness, and every built-in tool parameter is permanent schema surface plus path validation plus a sandbox fingerprint to keep in sync (#614 in this same batch is that fingerprint drifting out of sync once a tool takes a path).

Full reasoning: #623 (comment)

Thanks for the patch — the argument in the issue was well made, it just lands on the wrong side of "does this earn permanent tool surface".