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).

Watchdogs/System/conf_cache_watchdog.sh

@@ -5,7 +5,7 @@
 #
 # PURPOSE
 # ─────────────────────────────────────────────────────────────────────────────
-# Maintains the persistent partner conf backup at /boot/config/.cache/vv/d/.
+# Maintains the persistent partner conf backup at $PERSISTENT_CONF_CACHE.
 # Runs every 15 minutes via SYSTEM_WATCHDOG_SCRIPTS.
 #
 # When remote is OFFLINE:
@@ -33,7 +33,7 @@ require_partnership
 [[ -z "${REMOTE_ID:-}"         ]]            && exit 0
 
 RAM_CACHE="/tmp/.cache/vv/d"
-SAVE_DIR="/boot/config/.cache/vv/d"
+SAVE_DIR="$PERSISTENT_CONF_CACHE"
 
 if ping_remote; then
     if [[ -d "$SAVE_DIR" ]]; then