Expose commit hash in sarif blame output

[Copilot]

The sarif blame command now includes the commit hash/SHA in the blame information output. Previously, while the blame functionality extracted commit hashes from git blame --porcelain, it only exposed author information, timestamps, and commit messages without the actual commit identifier.

The commit hash is now available as a commit field in the blame properties:

{
  "properties": {
    "blame": {
      "commit": "915da616c17784840dd6b63e58aea0503e451264",
      "author": "Test User",
      "author-mail": "<test@example.com>",
      "author-time": "1756489481",
      "author-tz": "+0000",
      "committer": "Test User", 
      "committer-mail": "<test@example.com>",
      "committer-time": "1756489481",
      "committer-tz": "+0000",
      "summary": "Fix file format",
      "filename": "test.py"
    }
  }
}

This change also adds a commit filtering shortcut that maps to properties.blame.commit for easier filtering by commit hash.

The implementation is minimal and preserves all existing functionality while adding the requested commit hash information that was already being extracted internally.

Fixes #99.

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