Function scan_projects_dir 

pub fn scan_projects_dir(projects_dir: &Path) -> Result<Vec<SessionFile>>

Scan a projects directory for all session JSONL files.

This is the core scanner that works on any directory containing project subdirectories with JSONL session files. scan_claude_home delegates to this after appending projects/.

Directory structure expected:

projects_dir/
  <project>/
    <uuid>.jsonl              — main session
    agent-<id>.jsonl          — legacy agent
    <uuid>/subagents/agent-<id>.jsonl — new-style agent