Update all docs to reflect watchdog restructure
README-Watchdogs.md: new tier diagram, updated script table, execution flow,
state file table, and folder relationship diagram
Manual-Watchdogs.md: added system_watchdog (thin), System/storage_watchdog,
System/webgui_watchdog, and stability_watchdog sections; updated TOC and troubleshooting
README.md: updated schedule listing, folder description, daily cycle examples
README-User_Script_Plug-in.md: stability_watchdog references throughout
unRAID_Essentials/README + Manual: stability_watchdog, updated storage path
Monitors/README, Rsync/Manual, Tools/Manual: lock name list updates