Function get_changed_files 

pub fn get_changed_files(
    analysis_root: &Path,
    base_ref: &str,
) -> Result<HashSet<PathBuf>>

Returns the set of changed files as paths relative to analysis_root.

Resolves the git repo root internally so this works correctly even when analysis_root is a subdirectory of the repository (monorepo case).

Combines:

• git diff --name-only <base_ref> (committed changes vs base)
• git diff --name-only (unstaged changes)
• git ls-files --others --exclude-standard (untracked files)