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.

Deployment/host.conf.template

@@ -151,6 +151,11 @@
         # "my-Radarr.xml"
     )
 
+# XML templates pushed to mirror during onboard — other services (not auth, not arr).
+    HOSTN_PARTNERSHIP_SERVICES_STACK=(
+        # "my-Lidarr.xml"
+    )
+
 # Paths the partner should collect during the grace window after offboard.
     HOSTN_PARTNERSHIP_MIRROR_BACKUPS=(
         # "/mnt/user/appdata-Fallback/Partner-Emby"