Update from a fresh install of Debian 13.

Update from a fresh install of Debian 13.

Move Gate (and Core) to the private Ethernet immediately after
download (installing) additional packages, before exchanging public
keys, using their private IP addresses.

Punted the example of a textual Debian install setting the initial
user's password.  A graphical install is the default.

Added instructions for creating a WireGuard™ key pair and registering
the public key.  And gave the appropriate answers (the defaults) to
the Postfix installation questions.