Function detect_worktree 

pub fn detect_worktree(cwd: &Path) -> Result<Option<WorktreeInfo>, Error>

Detect if the given directory is within a git worktree.

Uses the provided cwd path to determine which worktree (if any) the directory belongs to. This avoids relying on process-global std::env::current_dir() which is unsafe in multi-threaded tests.

Returns:

• Ok(None) if not in a git repo or in the main worktree
• Ok(Some(WorktreeInfo)) if in a secondary worktree
• Err if there’s an error running git commands