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/services/ssh.py

@@ -17,8 +17,11 @@ class SSHService(BaseService):
     RFC 5424 via the rsyslog bridge baked into the image.
 
     service_cfg keys:
-        password      Root password (default: "admin")
-        hostname      Override container hostname
+        password         Root password (default: "admin")
+        user             Non-root user name (default: "ubuntu") for
+                         realistic "ssh user@host" lures + privesc capture
+        user_password    Non-root user's password (default: "admin")
+        hostname         Override container hostname
     """
 
     name = "ssh"
@@ -34,6 +37,33 @@ class SSHService(BaseService):
             secret=True,
             help="Plaintext root password for the in-container sshd.",
         ),
+        ServiceConfigField(
+            key="user",
+            label="Non-root user",
+            type="string",
+            default="ubuntu",
+            help=(
+                "Username for the second account on the decoy. Real Linux "
+                "boxes (especially Ubuntu cloud images) ship a non-root "
+                "admin user — having one makes the decoy more lifelike, "
+                "captures attackers who try `ssh user@host` for network "
+                "enumeration, and surfaces sudo/privesc behaviour the root-"
+                "only path misses."
+            ),
+        ),
+        ServiceConfigField(
+            key="user_password",
+            label="Non-root user password",
+            type="password",
+            default="admin",
+            secret=True,
+            help=(
+                "Password for the non-root user. Captured at PAM auth time "
+                "via the same auth-helper that handles root logins. The "
+                "user is in the `sudo` group; subsequent privesc attempts "
+                "fan out through the existing sudo-log capture."
+            ),
+        ),
         ServiceConfigField(
             key="hostname",
             label="Container hostname",
@@ -55,6 +85,13 @@ class SSHService(BaseService):
         cfg = service_cfg or {}
         env: dict = {
             "SSH_ROOT_PASSWORD": cfg.get("password", "admin"),
+            # Non-root user account — created at runtime by the entrypoint
+            # iff SSH_USER is non-empty. Defaults to "ubuntu"/"admin" so
+            # `ssh ubuntu@<decky>` works out of the box (the conventional
+            # cloud-init account on Ubuntu cloud images, very low-friction
+            # for attackers running ssh enumeration scripts).
+            "SSH_USER": cfg.get("user", "ubuntu"),
+            "SSH_USER_PASSWORD": cfg.get("user_password", "admin"),
             # NODE_NAME is the authoritative decky identifier for log
             # attribution — matches the host path used for the artifacts
             # bind mount below. The container hostname (optionally overridden