Function parse_gitai_note 

pub fn parse_gitai_note(note: &str) -> Option<GitAiAuthorshipLog>

Parse a git-ai note (from git notes --ref refs/notes/ai show <sha>).

Format (v3.0.0):

path/to/file.rs
   session_id 94,102,107,120,122-123,128
another/file.rs
   session_id 1-5,10
---
{"schema_version":"authorship/3.0.0",...}

Line specs are comma-separated numbers and ranges (no +/- prefix).