Create a passive mode

Passive mode will not identify hosts by scanning IP ranges or targets files. Instead, this will attempt to identify hosts by passively monitoring broadcast activity for new hosts. It would then log these hosts to a file and scan any available shares unless previously added/scanned.

Start by reviewing the repository's Python entry points and current host and share-scanning flow. Determine how passive broadcast monitoring, host logging, and avoiding previously scanned hosts would fit together. Done means newly observed hosts are logged and available shares are scanned without repeating prior work.

Written by the indexing model from the issue text.