fix(deploy): wire per-unit log files on master systemd services

The agent-side enroll-bundle templates (decnet/web/templates/*) always
set DECNET_SYSTEM_LOGS + StandardOutput/StandardError to a per-unit
file under /var/log/decnet. The master-side init templates (deploy/*)
never did, so every 'decnet init'-installed service:

- inherited the default DECNET_SYSTEM_LOGS=decnet.system.log — a
  relative path, landing in the unit's WorkingDirectory. All 13 units
  shared the same cwd and fought for the same file, or more often
  just failed to write it under ProtectSystem=full,
- emitted stdout/stderr to the journal by default, which is fine for
  uvicorn's INFO banter but makes per-service grepping a pain when
  you're chasing a single worker's trace.

Mirror the agent-side wiring on all 13 master templates:
- Environment=DECNET_SYSTEM_LOGS=/var/log/decnet/decnet.<name>.log
- StandardOutput=append:/var/log/decnet/decnet.<name>.log
- StandardError=append:/var/log/decnet/decnet.<name>.log

/var/log/decnet is already in ReadWritePaths so ProtectSystem=full
stays compatible. Operators now get a dedicated
/var/log/decnet/decnet.<unit>.log per service, both from the app's
structured logger and from any stray stderr — journalctl still
works too, but no longer the only option.

deploy/decnet-forwarder.service.j2

@@ -15,7 +15,10 @@ EnvironmentFile=-{{ install_dir }}/.env.local
 # Replace <master-host> with the master's LAN address or hostname. The agent
 # cert bundle at /etc/decnet/agent is reused — the forwarder presents the same
 # worker identity when it connects to the master's listener.
+Environment=DECNET_SYSTEM_LOGS=/var/log/decnet/decnet.forwarder.log
 ExecStart={{ venv_dir }}/bin/decnet forwarder \
+StandardOutput=append:/var/log/decnet/decnet.forwarder.log
+StandardError=append:/var/log/decnet/decnet.forwarder.log
     --log-file /var/log/decnet/decnet.log \
     --master-host ${DECNET_SWARM_MASTER_HOST} \
     --master-port 6514 \