Wire up unused config vars found in follow-up audit pass

TRANSCODE_LOG_RETENTION was documented as trimming the daily transcode log
but never referenced — log grew unbounded. TRANSCODE_ORPHAN_AGE was shown in
--status but never used, so empty session folders were deleted immediately
instead of after the documented grace period, risking a race against ffmpeg
creating a folder just before writing its first segment.

docker_watchdog.sh's daemon-health thresholds were only hardcoded fallbacks
despite comments claiming they were master.conf-configurable, and it
referenced a heartbeat feature that was never implemented (that's owned by
watchdog_orchestrator.sh, its caller) — added the three thresholds to
master.conf for real and removed the stale heartbeat claim.

Also added the missing HOSTN_PARTNERSHIP_SERVICES_STACK block to
host.conf.template (containers.sh already read it via detect_hosts, just
never had a template entry) and corrected play_state_sync.sh's doc comment
for PLAY_SYNC_TYPES' actual default.

Media/play_state_sync.sh

@@ -79,7 +79,8 @@
 #                            false = local servers only (this host's Emby + Jellyfin)
 #   PLAY_SYNC_DAYS           How many days back to check for played items (default: 90)
 #                            Use 0 to sync all played items (slow on large libraries).
-#   PLAY_SYNC_TYPES          Comma-separated item types to sync (default: Movie,Episode,Audio)
+#   PLAY_SYNC_TYPES          Comma-separated item types to sync (default: Movie,Episode —
+#                            Audio excluded, music library too large; favorites handled separately)
 #
 # ==============================================================================================
 # RUNTIME MODES