Add /pp list --all to show unrecognized JARs

Add an opt-in `--all` switch to `/pp list` that also shows JAR files in the server plugins directory which Plugin Portal does not recognize or track.

Keep the existing default list focused on recognized/tracked plugins. The expanded view should make it clear which entries are unrecognized.

Credit to Zoriot.

Start at the `/pp list` command and trace how it currently finds recognized plugins. Then inspect how the server plugins directory is read; done means the default list remains unchanged while `/pp list --all` includes unrecognized JARs and clearly labels them.

Written by the indexing model from the issue text.