feat(ssh,telnet): add non-root user account for privesc + enum lure

Real Linux deployments (especially Ubuntu cloud images) ship a non-
root admin user; honeypots that only accept root logins are a tell.
Add a second account on both SSH and Telnet decoys, configurable
via service_cfg keys `user` / `user_password`, defaulting to
`ubuntu` / `admin` so the lure is live on every fresh deploy.

* `decnet/services/{ssh,telnet}.py` — two new ServiceConfigFields
  (`user` string, `user_password` secret) and matching env vars
  (`SSH_USER` / `SSH_USER_PASSWORD`, mirror for telnet) propagated
  via the compose fragment.
* `decnet/templates/ssh/entrypoint.sh` — runtime `useradd -m -s
  /usr/libexec/login-session -G sudo "$SSH_USER"` so the new user
  inherits the same sessrec pty-recording shell as root and lands
  in the sudo group. Privesc attempts (`sudo`) flow through the
  existing sudo-log capture; network-enum from the user's shell
  rides the recorded transcript.
* `decnet/templates/telnet/entrypoint.sh` — same useradd pattern
  (no sudo group — busybox+login telnet image has no sudo
  package; privesc rides `su -` which itself flows through the
  existing PAM auth-helper at /etc/pam.d/login).
* New tests for default + custom user / password + independence
  from root password. Updated the schema-keys assertion to match
  the four-field shape.

The new account is ALSO the natural home for the body-aware
predicates that were previously gated on root-only sessions —
attackers who land on `ubuntu@host` and run network-recon /
privesc commands now generate the same structured TTP-rule
events as root sessions did, captured via the same auth-helper
+ sessrec + sudo-log pipes.

decnet/templates/ssh/entrypoint.sh

@@ -5,6 +5,26 @@ set -e
 ROOT_PASSWORD="${SSH_ROOT_PASSWORD:-admin}"
 echo "root:${ROOT_PASSWORD}" | chpasswd
 
+# Non-root user — gives the decoy a realistic "ssh user@host" surface
+# so attackers running enumeration scripts find a plausible second
+# account, AND so post-login privesc (sudo) flows through the
+# existing sudo-log capture pipe. SSH_USER blank means "no second
+# user" (legacy single-account behaviour); the compose fragment
+# defaults SSH_USER to "ubuntu" so this branch is the live path on
+# fresh deploys.
+SSH_USER="${SSH_USER:-}"
+SSH_USER_PASSWORD="${SSH_USER_PASSWORD:-admin}"
+if [ -n "${SSH_USER}" ] && [ "${SSH_USER}" != "root" ]; then
+    if ! id -u "${SSH_USER}" >/dev/null 2>&1; then
+        # Login shell points at the same sessrec wrapper root uses,
+        # so the new user's pty session is recorded — privesc and
+        # network-enum behaviour ride the existing capture pipe
+        # without a parallel implementation.
+        useradd -m -s /usr/libexec/login-session -G sudo "${SSH_USER}"
+    fi
+    echo "${SSH_USER}:${SSH_USER_PASSWORD}" | chpasswd
+fi
+
 # Optional: override hostname inside container
 if [ -n "$SSH_HOSTNAME" ]; then
     echo "$SSH_HOSTNAME" > /etc/hostname