Storage-mode awareness pass + doc update for System_Essentials through Partnership

All state/data file paths in scripts and PHP now resolve via STATE_DIR / DATA_DIR /
PERSISTENT_CONF_CACHE instead of hardcoded /boot/config/ or /tmp/ paths, so the
ecosystem works in both internal and appdata storage modes.

PHP layer (watchdog.php, partnership.php, fallback.php, monitor.php, snapshot.php,
config.php): all state reads switched to STATE_DIR constant; remote state reads use
the new vv_remote_state_cmd() helper which resolves the remote's SCRIPTS_DIR via
their varaverk.cfg before building the path.

conf_sync.sh: fixed SCRIPTS_ROOT → SCRIPTS_DIR bug on MY_CONF path; added
_remote_scripts_dir() to resolve partner's SCRIPTS_DIR before SCP pull.

fallback.php page: added controls card (PARTNERSHIP_ENABLED, FALLBACK_ENABLED,
FALLBACK_RSYNC_ENABLED toggles), status grid, and settings card.

README and Manual updated for System_Essentials, Watchdogs, Fallback, Rsync,
Media, Monitors, Orchestrators, Partnership: added new scripts (conf_sync,
conf_cache_save/restore, conf_cache_watchdog, play_state_sync, start_webhook_listener,
upgrade_webhook_handler), corrected all stale /boot/config/ state file paths to
$STATE_DIR/$DATA_DIR, noted webgui/php_fpm/mover/user_scripts scripts moved to
Plugin/unraid/System_Essentials, fixed start_webhook_listener.sh header (Node.js,
not PHP -S).

System_Essentials/conf_cache_save.sh

@@ -5,7 +5,7 @@
 #
 # PURPOSE
 # ─────────────────────────────────────────────────────────────────────────────
-# Snapshots the partner conf RAM cache to /boot/config/.cache/vv/d/ on
+# Snapshots the partner conf RAM cache to $PERSISTENT_CONF_CACHE on
 # array stop. Survives reboot. Used by conf_cache_restore.sh at next array start
 # to reload partner vars into RAM when the partner is unreachable at boot time.
 #
@@ -15,7 +15,7 @@
 # down, the backup fills the gap so fallback.sh has the vars it needs.
 #
 # Only partner confs are saved — own conf is always on disk.
-# Location is outside the git repo and outside the main plugin folder.
+# Path adapts to storage mode: $SCRIPTS_DIR/.cache/vv/d (internal or appdata).
 # ==============================================================================================
 
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
@@ -26,7 +26,7 @@ detect_hosts
 require_partnership
 
 RAM_CACHE="/tmp/.cache/vv/d"
-SAVE_DIR="/boot/config/.cache/vv/d"
+SAVE_DIR="$PERSISTENT_CONF_CACHE"
 
 [[ "$DRY_RUN" == true ]] && warn "DRY RUN — no files will be written"