Adds third-party script warning with user confirmation before running
the upstream installer (install) and updater (update), matching the
kasm/pihole pattern. Removes redundant binary existence check per
reviewer feedback. Adds corresponding JSON warning note.
- default_credentials: username null/null (no SSH login for hermes
service account; access is via root like all PVE Helper Scripts)
- Update setup note to reference root instead of hermes user
- Update dashboard tunnel note to use root and -fNL flags
