feat: add fallback.sh --stop for clean array shutdown

Fallback runs as a bare subprocess (cmdline: bash .../Fallback/fallback.sh),
not via /tmp/user.scripts, so user_scripts_stop.sh cannot find it.
Adding --stop mode closes that gap in the array shutdown sequence.

fallback.sh --stop: reads lock file (/tmp/unraid_locks/fallback.lock) to
get the running PID, sends SIGTERM (hits the existing trap that sets
FALLBACK_RUNNING=false), waits up to 10s, SIGKILLs if still alive.

master.conf: insert Fallback/fallback.sh --stop as step 2 in
ARRAY_STOP_SCRIPTS (after user_scripts_stop, before rsync_stop).

user_script_plug-in.sh: update ARRAY STOPPING block to show 5-step order
and add v2.5 changelog entry.

master.conf

@@ -201,10 +201,10 @@
     PARTNERSHIP_ONBOARD_NOTIFY=true         # notify both servers on completion
     PARTNERSHIP_SYNC_INTERVAL=15            # minutes — informational, actual schedule in cron
 
-# SSH key lifecycle — managed by Initial_run/ssh_setup.sh.
+# SSH key lifecycle — managed by Partnership/ssh_setup.sh.
 # Key named after this server: hostname lowercased, unraid- prefix stripped.
 #   unRAID-Gmer4Lfe → /root/.ssh/gmer4lfe_rsync_automation
-# Run Initial_run/partnership_onboard.sh to generate, copy, and update conf automatically.
+# Run Partnership/partnership_onboard.sh to generate, copy, and update conf automatically.
     SSH_MAX_STRIKES=5                       # consecutive SSH auth failures before critical notify
     SSH_STRIKE_RESET_HRS=24                 # hours since last failure before strike counter resets
 
@@ -269,6 +269,7 @@
 # Order matters: user scripts first (prevents new ops), then data movement, then containers.
     ARRAY_STOP_SCRIPTS=(
         "unRAID_Essentials/user_scripts_stop.sh"        # stop background scripts before they start new ops
+        "Fallback/fallback.sh --stop"                   # gracefully stop fallback (not caught by user_scripts_stop)
         "unRAID_Essentials/rsync_stop.sh --rsync-only"  # kill rsync; skip container recovery (handled below)
         "unRAID_Essentials/mover_stop.sh"               # stop mover after rsync (they conflict on same files)
         "Docker_Essentials/docker_container_stop.sh"    # stop all containers last