refactor: strip DECNET tokens from container-visible surface

Rename the container-side logging module decnet_logging → syslog_bridge
(canonical at templates/syslog_bridge.py, synced into each template by
the deployer). Drop the stale per-template copies; setuptools find was
picking them up anyway. Swap useradd/USER/chown "decnet" for "logrelay"
so no obvious token appears in the rendered container image.

Apply the same cloaking pattern to the telnet template that SSH got:
syslog pipe moves to /run/systemd/journal/syslog-relay and the relay
is cat'd via exec -a "systemd-journal-fwd". rsyslog.d conf rename
99-decnet.conf → 50-journal-forward.conf. SSH capture script:
/var/decnet/captured → /var/lib/systemd/coredump (real systemd path),
logger tag decnet-capture → systemd-journal. Compose volume updated
to match the new in-container quarantine path.

SD element ID shifts decnet@55555 → relay@55555; synced across
collector, parser, sniffer, prober, formatter, tests, and docs so the
host-side pipeline still matches what containers emit.

templates/postgres/server.py

@@ -9,7 +9,7 @@ returns an error. Logs all interactions as JSON.
 import asyncio
 import os
 import struct
-from decnet_logging import syslog_line, write_syslog_file, forward_syslog
+from syslog_bridge import syslog_line, write_syslog_file, forward_syslog
 
 NODE_NAME = os.environ.get("NODE_NAME", "pgserver")
 SERVICE_NAME   = "postgres"