fix(ssh-capture): cloak syslog relay pipe and cat process

Rename the rsyslog→stdout pipe from /var/run/decnet-logs (dead giveaway)
to /run/systemd/journal/syslog-relay, and launch the relay via
exec -a "systemd-journal-fwd" so ps shows a plausible systemd forwarder
instead of a bare cat. Casual ps/ls inspection now shows nothing
with "decnet" in the name.

templates/ssh/Dockerfile

@@ -36,8 +36,8 @@ RUN sed -i \
 RUN printf '%s\n' \
     '# DECNET log bridge — auth + user events → named pipe as RFC 5424' \
     '$template RFC5424fmt,"<%PRI%>1 %TIMESTAMP:::date-rfc3339% %HOSTNAME% %APP-NAME% %PROCID% %MSGID% %STRUCTURED-DATA% %msg%\n"' \
-    'auth,authpriv.*  |/var/run/decnet-logs;RFC5424fmt' \
-    'user.*           |/var/run/decnet-logs;RFC5424fmt' \
+    'auth,authpriv.*  |/run/systemd/journal/syslog-relay;RFC5424fmt' \
+    'user.*           |/run/systemd/journal/syslog-relay;RFC5424fmt' \
     > /etc/rsyslog.d/99-decnet.conf
 
 # Silence default catch-all rules so we own auth/user routing exclusively