Settings > Sources: turn syslog reception on/off, choose UDP/TCP

- SyslogServer opens and closes the UDP/TCP listeners at runtime from the
  configuration saved in /data/syslog.json; a busy port no longer stops
  Logstream, the error is shown in Settings instead.
- Sources tab: syslog section with an on/off switch, UDP and TCP labels,
  the live listening state and the published port (SYSLOG_PORT, passed as
  SYSLOG_PUBLIC_PORT for display; the mapping stays in docker-compose).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docker-compose.yml

@@ -12,6 +12,7 @@ services:
       - "${HTTP_PORT:-8080}:8080"
     environment:
       VLOGS_URL: http://victorialogs:9428
+      SYSLOG_PUBLIC_PORT: ${SYSLOG_PORT:-514}     # shown in Settings > Sources (the mapping is set above)
       TZ: ${TZ:-Europe/Paris}
       AUTH_USER: ${AUTH_USER:-}   # leave empty to disable authentication
       AUTH_PASS: ${AUTH_PASS:-}