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.

decnet/engine/deployer.py

@@ -31,11 +31,11 @@ from decnet.network import (
 log = get_logger("engine")
 console = Console()
 COMPOSE_FILE = Path("decnet-compose.yml")
-_CANONICAL_LOGGING = Path(__file__).parent.parent.parent / "templates" / "decnet_logging.py"
+_CANONICAL_LOGGING = Path(__file__).parent.parent.parent / "templates" / "syslog_bridge.py"
 
 
 def _sync_logging_helper(config: DecnetConfig) -> None:
-    """Copy the canonical decnet_logging.py into every active template build context."""
+    """Copy the canonical syslog_bridge.py into every active template build context."""
     from decnet.services.registry import get_service
     seen: set[Path] = set()
     for decky in config.deckies:
@@ -47,7 +47,7 @@ def _sync_logging_helper(config: DecnetConfig) -> None:
             if ctx is None or ctx in seen:
                 continue
             seen.add(ctx)
-            dest = ctx / "decnet_logging.py"
+            dest = ctx / "syslog_bridge.py"
             if not dest.exists() or dest.read_bytes() != _CANONICAL_LOGGING.read_bytes():
                 shutil.copy2(_CANONICAL_LOGGING, dest)