Fix host-side Git commit identity

[eshulman2]

Summary

• configure the Git committer identity per host-side commit using the existing Forge Git settings
• use the configured Git email for the explicit author identity
• add a regression test that commits with an empty global Git configuration and verifies author and committer metadata

Root cause

AISOS-2385 exposed that GitOperations.commit() supplied --author but relied on the worker service account's global Git configuration for the committer. On workers without that configuration, Git failed with Committer identity unknown, leaving dirty workspaces and triggering workspace recovery failures.

Testing

• uv run ruff check src/forge/workspace/git_ops.py tests/unit/workspace/test_git_ops_commit.py
• uv run pytest tests/unit/workspace/test_git_ops_commit.py tests/unit/workspace/test_git_ops_sync.py tests/unit/workspace/test_git_ops_redaction.py (6 passed)