feat(deploy): systemd unit for decnet-reuse-correlator

Adds the systemd template for the credential-reuse correlator daemon
and wires it into decnet.target so `decnet init` installs it
automatically (the unit installer globs decnet-*.service.j2). Mirrors
the mutator template: bus-woken Type=simple service with the standard
hardening + on-failure restart.

Also registers `reuse-correlator` in the in-process worker registry
(so the dashboard panel surfaces its heartbeat instead of dropping it
as unknown) and slots it into the start-all preferred order between
mutator and webhook.

decnet/web/router/workers/api_start_all_workers.py

@@ -25,6 +25,7 @@ _PREFERRED_ORDER: tuple[str, ...] = (
     "sniffer",
     "prober",
     "mutator",
+    "reuse-correlator",
     "webhook",
 )
 

decnet/web/worker_registry.py

@@ -38,6 +38,7 @@ KNOWN_WORKERS: tuple[str, ...] = (
     "sniffer",
     "prober",
     "mutator",
+    "reuse-correlator",  # credential-reuse pass — bus-woken on credential.captured
     "webhook",    # external SIEM/SOAR egress — bus consumer → HMAC HTTP POSTs
     "agent",
     "forwarder",