doc audit — fix stale watchdog vars, fallback_state_reset, add monthly_maintenance and mesh_monitor sections

- Tools/Manual-Tools.md: fallback_state_reset.sh marked not yet built; manual
  workaround added; TOC entry updated; failover→fallback rename throughout
- Watchdogs/Manual-Watchdogs.md: System Watchdog config block updated — remove
  pre-split vars (MEM_WARN_GB, MEM_SHUTDOWN_GB, MEM_GB, MEM_RECOVER_GB,
  SYS_WATCHDOG_MEM_SHUTDOWN_EXCLUDED, SYS_WATCHDOG_REQUIRED_CONTAINERS);
  add SYS_WATCHDOG_MEM_GB (reboot trigger only); fix state file path names
  (watchdog_state.db → container_watchdog_state.db,
  sys_watchdog_state.db → system_watchdog_state.db)
- Orchestrators/README-Orchestrators.md: add monthly_maintenance.sh section
  with two-gate model, configuration reference, and usage examples
- Monitors/README-Monitors.md: add mesh_monitor.sh to both tables and diagram
- Monitors/Manual-Monitors.md: add mesh_monitor.sh section
- README-User_Script_Plug-in.md, Rsync/README-Rsync.md, Rsync/Manual-Rsync.md,
  README.md: emby-failover → emby-fallback (missed from prior batch)

Orchestrators/README-Orchestrators.md

@@ -104,7 +104,7 @@ array_started.sh
 # Cron — one entry per maintenance window:
 */3   * * * *    transcode_management.sh
 0  */6 * * *     arrs_failed_stalled_recovery.sh
-*/30  * * * *    rsync.sh emby-failover          ← not an orchestrator, direct call
+*/30  * * * *    rsync.sh emby-fallback          ← not an orchestrator, direct call
 0   1 * * *      daily_sync_maintenance.sh
 30  2 * * 0      weekly_sync_maintenance.sh
 
@@ -730,7 +730,7 @@ maintenance block before the 7am coffee report.
 # ─────────────────────────────────────────────────────────────────────────────
 # Two Emby syncs run in parallel — dirty and clean:
 #
-# emby-failover dirty sync (every 30 minutes, Emby running):
+# emby-fallback dirty sync (every 30 minutes, Emby running):
 #   watch states, library deltas, user activity — continuous coverage
 #   WAL files excluded — safe to copy while Emby writes
 #   HOST2 always within 30 minutes of HOST1 on playback state
@@ -838,6 +838,50 @@ weekly_sync_maintenance.sh --status     # show configured shares, jobs, update t
 
 ---
 
+## ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+## 📆  monthly_maintenance.sh
+## ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+Uptime-triggered orchestrator for long-running system tasks — ZFS scrub, SMART
+long tests — that should only run on stable systems that have been up for at least
+30 days. Called daily by cron; most invocations are silent no-ops.
+
+Two gates must both pass before any job runs:
+1. Server uptime ≥ `MONTHLY_UPTIME_THRESHOLD_DAYS`
+2. Last run ≥ `MONTHLY_RUN_INTERVAL_DAYS` ago (state file on `/boot/config/` — survives reboots)
+
+If either gate fails, the script exits 0 with no output. This is expected — it runs
+daily and most days are no-ops.
+
+`--force` bypasses both gates and runs the job list immediately. Use for testing or
+when a scrub was missed and the server hasn't reached the uptime threshold yet.
+
+### Configuration (master.conf)
+
+```bash
+MONTHLY_MAINTENANCE_SCRIPTS=(
+    #"Tools/zfs_pool_scrub.sh"
+    #"Tools/smart_long_test.sh"
+)
+MONTHLY_UPTIME_THRESHOLD_DAYS=30
+MONTHLY_RUN_INTERVAL_DAYS=30
+MONTHLY_LAST_RUN_FILE="/boot/config/monthly_maintenance_last_run.db"
+```
+
+Scripts are commented out by default — uncomment what applies to your hardware.
+
+### Usage
+
+```bash
+monthly_maintenance.sh              # normal run (daily cron — silent no-op when gates not met)
+monthly_maintenance.sh --force      # bypass both gates — run immediately
+monthly_maintenance.sh --dry-run    # show what would run without running it
+monthly_maintenance.sh --status     # show gate state: uptime, last run, next eligible
+monthly_maintenance.sh --log        # verbose output from each child script
+```
+
+---
+
 ## ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
 ## 🧹  media_management.sh
 ## ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
@@ -906,7 +950,7 @@ array_started.sh
 # ─────────────────────────────────────────────────────────────────────────────
 # Periodic — not an orchestrator, direct rsync call:
 # ─────────────────────────────────────────────────────────────────────────────
-*/30 * * * *    rsync.sh /mnt/user/Media_Server/Emby --profile=emby-failover
+*/30 * * * *    rsync.sh /mnt/user/Media_Server/Emby --profile=emby-fallback
 
 # ─────────────────────────────────────────────────────────────────────────────
 # Every 6 hours: