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)

Rsync/README-Rsync.md

@@ -68,7 +68,7 @@ Orchestrators/                 ← decides what to sync, when, and in what order
   critical_sync_maintenance.sh ────────────────────────────────► rsync.sh (partnership shares)
 
 Cron (direct):
-  */30 * * * *               ──────────────────────────────────► rsync.sh --profile=emby-failover
+  */30 * * * *               ──────────────────────────────────► rsync.sh --profile=emby-fallback
 
 Monitors/
   bandwidth_monitor.sh       ◄─── called by rsync.sh after each sync (--log-transfer)
@@ -94,7 +94,7 @@ Profile key = directory basename lowercased. `--profile=name` overrides.
 | `critical-data` | Auth stack | Mariadb-Authelia, Redis-Authelia, NPM, Lldap | Authelia has restart delay |
 | `important-data` | NextCloud + Postgres | Postgres-NextCloud | NextCloud has restart delay |
 | `emby` | Full Emby mirror | Emby (both sides) | Weekly — Sunday 2:30am |
-| `emby-failover` | Emby watch state delta | None | Dirty sync — Emby stays running |
+| `emby-fallback` | Emby watch state delta | None | Dirty sync — Emby stays running |
 
 For full profile definitions see `Manual-Rsync.md`.
 
@@ -116,7 +116,7 @@ Callers (Orchestrators/) ──────────────────
   weekly_sync_maintenance.sh         rsync.sh /path/to/share [--profile=name]  │
   critical_sync_maintenance.sh  ─────────────────────────────────────────────► │
   fallback.sh (writeback)                                                       │
-  Direct cron (emby-failover)                                                   │
+  Direct cron (emby-fallback)                                                   │
                                                                                 ▼
                                             ┌─────────────────────────────────────┐
                                             │  1. Infer/accept profile             │