Add workspace dir + clean up junk from project root ...

- workspace/ — persistent dir for Navi's long-term files (scripts, notes,
  data); excluded from git, Navi instructed to use it instead of project root
- .gitignore: session_files/ and workspace/* added
- persona.txt: WORKSPACE section pointing Navi to workspace/
- Deleted scanner.py, network_scan_results.txt, targets.txt (Navi artifacts)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>