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/telnet/entrypoint.sh

@@ -5,6 +5,23 @@ set -e
 ROOT_PASSWORD="${TELNET_ROOT_PASSWORD:-admin}"
 echo "root:${ROOT_PASSWORD}" | chpasswd
 
+# Non-root user — gives the decoy a realistic "telnet user@host"
+# surface so enumeration scripts that only try common usernames find
+# a plausible second account, AND so post-login `su -` privesc flows
+# through the existing PAM auth-helper. Login shell is the sessrec
+# wrapper so the user's pty session is recorded in the same shape
+# as root's. TELNET_USER blank disables the second account; the
+# compose fragment defaults TELNET_USER to "ubuntu" so this branch
+# is the live path on fresh deploys.
+TELNET_USER="${TELNET_USER:-}"
+TELNET_USER_PASSWORD="${TELNET_USER_PASSWORD:-admin}"
+if [ -n "${TELNET_USER}" ] && [ "${TELNET_USER}" != "root" ]; then
+    if ! id -u "${TELNET_USER}" >/dev/null 2>&1; then
+        useradd -m -s /usr/libexec/login-session "${TELNET_USER}"
+    fi
+    echo "${TELNET_USER}:${TELNET_USER_PASSWORD}" | chpasswd
+fi
+
 # Optional: override hostname inside container
 if [ -n "$TELNET_HOSTNAME" ]; then
     echo "$TELNET_HOSTNAME" > /etc/hostname