feat(ssh): replace Cowrie with real OpenSSH + rsyslog logging pipeline

Scraps the Cowrie emulation layer. The real_ssh template now runs a
genuine sshd backed by a three-layer logging stack forwarded to stdout
as RFC 5424 for the DECNET collector:

  auth,authpriv.*  → rsyslogd → named pipe → stdout  (logins/failures)
  user.*           → rsyslogd → named pipe → stdout  (PROMPT_COMMAND cmds)
  sudo syslog=auth → rsyslogd → named pipe → stdout  (privilege escalation)
  sudo logfile     → /var/log/sudo.log               (local backup with I/O)

The ssh.py service plugin now points to templates/real_ssh and drops all
COWRIE_* / NODE_NAME env vars, sharing the same compose fragment shape as
real_ssh.py.

tests/test_ssh.py

@@ -0,0 +1,90 @@
+"""
+Tests for the SSHService plugin (real OpenSSH, Cowrie removed).
+"""
+
+from decnet.services.registry import all_services, get_service
+
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+def _fragment(service_cfg: dict | None = None, log_target: str | None = None) -> dict:
+    return get_service("ssh").compose_fragment(
+        "test-decky", log_target=log_target, service_cfg=service_cfg
+    )
+
+
+# ---------------------------------------------------------------------------
+# Registration
+# ---------------------------------------------------------------------------
+
+def test_ssh_registered():
+    assert "ssh" in all_services()
+
+
+def test_ssh_ports():
+    assert get_service("ssh").ports == [22]
+
+
+def test_ssh_is_build_service():
+    assert get_service("ssh").default_image == "build"
+
+
+def test_ssh_dockerfile_context_exists():
+    svc = get_service("ssh")
+    ctx = svc.dockerfile_context()
+    assert ctx.is_dir(), f"Dockerfile context missing: {ctx}"
+    assert (ctx / "Dockerfile").exists()
+    assert (ctx / "entrypoint.sh").exists()
+
+
+# ---------------------------------------------------------------------------
+# No Cowrie env vars
+# ---------------------------------------------------------------------------
+
+def test_no_cowrie_vars():
+    env = _fragment()["environment"]
+    cowrie_keys = [k for k in env if k.startswith("COWRIE_") or k == "NODE_NAME"]
+    assert cowrie_keys == [], f"Unexpected Cowrie vars: {cowrie_keys}"
+
+
+# ---------------------------------------------------------------------------
+# compose_fragment structure
+# ---------------------------------------------------------------------------
+
+def test_fragment_has_build():
+    frag = _fragment()
+    assert "build" in frag and "context" in frag["build"]
+
+
+def test_fragment_container_name():
+    assert _fragment()["container_name"] == "test-decky-ssh"
+
+
+def test_fragment_restart_policy():
+    assert _fragment()["restart"] == "unless-stopped"
+
+
+def test_fragment_cap_add():
+    assert "NET_BIND_SERVICE" in _fragment().get("cap_add", [])
+
+
+def test_default_password():
+    assert _fragment()["environment"]["SSH_ROOT_PASSWORD"] == "admin"
+
+
+def test_custom_password():
+    assert _fragment(service_cfg={"password": "h4x!"})["environment"]["SSH_ROOT_PASSWORD"] == "h4x!"
+
+
+def test_custom_hostname():
+    assert _fragment(service_cfg={"hostname": "prod-db-01"})["environment"]["SSH_HOSTNAME"] == "prod-db-01"
+
+
+def test_no_hostname_by_default():
+    assert "SSH_HOSTNAME" not in _fragment()["environment"]
+
+
+def test_no_log_target_in_env():
+    assert "LOG_TARGET" not in _fragment(log_target="10.0.0.1:5140").get("environment", {})