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.

tests/test_cli.py

@@ -316,7 +316,7 @@ class TestCorrelateCommand:
         log_file = tmp_path / "test.log"
         log_file.write_text(
             "<134>1 2024-01-15T12:00:00+00:00 decky-01 ssh - auth "
-            '[decnet@55555 src_ip="10.0.0.5" username="admin"] login\n'
+            '[relay@55555 src_ip="10.0.0.5" username="admin"] login\n'
         )
         result = runner.invoke(app, ["correlate", "--log-file", str(log_file)])
         assert result.exit_code == 0