rename appdata-Failover→appdata-Fallback in docs; critical sync 15→30min; transcode 3→7min

appdata-Failover → appdata-Fallback:
  All .md files updated — scripts and confs already used appdata-Fallback.
  Share was renamed; docs were the only stale references.

critical_sync_maintenance.sh: */15 → */30, 96/day → 48/day:
  critical_sync_maintenance.sh header, master.conf, host1/2.conf comments,
  Orchestrators README, User Script Plug-in README, Partnership README/manual/script,
  Docker_Essentials README/downloaders_reset.sh, Fallback README,
  weekly_sync_maintenance.sh, user_script_plug-in.sh all updated.

rsync_emby_failover User Script superseded:
  Emby dirty sync was already in HOST1_CRITICAL_SYNC_SHARES — it now runs inside
  critical_sync_maintenance.sh every 30min alongside auth sync and partnership check.
  Section in User Script Plug-in README marked for deletion from plugin.

transcode_management.sh: */3 → */7:
  transcode_management.sh, transcode_manager.sh, transcode_cleanup.sh headers,
  Transcodes README/manual, Orchestrators README, User Script Plug-in README,
  user_script_plug-in.sh all updated.

Docker_Essentials/downloaders_reset.sh

@@ -9,7 +9,7 @@
 # state that download clients generate but never clean up themselves — stuck
 # searches, dead transfers, failed imports, stale queue entries, completed history.
 #
-# Called every 15 minutes by critical_sync_maintenance.sh via
+# Called every 30 minutes by critical_sync_maintenance.sh via
 # CRITICAL_MAINTENANCE_SCRIPTS. Can also be run manually for ad hoc cleanup.
 # If a downloader is not configured for this host, that section skips cleanly.
 #
@@ -137,7 +137,7 @@ if [[ "$EUID" -ne 0 ]]; then
     exit 1
 fi
 
-# Lock first — wait mode since this runs every 15min and previous may still be finishing
+# Lock first — wait mode since this runs every 30min and previous may still be finishing
 acquire_lock "wait"
 
 # detect_hosts() sets MY_ID and aliases all HOST*_SLSKD_*, HOST*_SABNZBD_*, HOST*_QBIT_* vars