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)

README-User_Script_Plug-in.md

@@ -296,7 +296,7 @@ Background: YES
 ```bash
 #!/bin/bash
 /mnt/user/appdata/unraid_scripts/Rsync/rsync.sh \
-    /mnt/user/Media_Server/Emby --profile=emby-failover
+    /mnt/user/Media_Server/Emby --profile=emby-fallback
 ```
 
 **What it does:**
@@ -304,7 +304,7 @@ Keeps HOST2's Emby within 30 minutes of HOST1 on watch states, play positions, a
 library changes — with Emby running on both sides. Not a full sync (that's weekly) —
 this is continuous coverage of what matters for failover.
 
-**What syncs (emby-failover profile):**
+**What syncs (emby-fallback profile):**
 ```
 Syncs:     users.db, library.db, authentication.db, config/
 Skips:     *.wal *.shm  — WAL files being written by Emby, unsafe to copy mid-write
@@ -800,7 +800,7 @@ Background: YES
 
 **What syncs:** full clean Emby mirror — all databases checkpointed, metadata, plugins,
 config. Both Emby instances stopped during sync. Excludes transcodes, logs, cache, crash
-files. This is the full-fidelity sync (vs emby-failover which is the dirty 30-minute sync).
+files. This is the full-fidelity sync (vs emby-fallback which is the dirty 30-minute sync).
 
 ---