fix monitor disk used space underreported for spun-down disks

Unraid API returns fsUsed=0 when a disk's filesystem is unmounted (spun
down). disks.ini keeps the last-known value in KB even after spindown —
use it as fallback when isSpinning=false and fsUsed=0. Also remove the
mounted-only guard in the ini fallback path (vv_disk_entry) for the same
reason. Stale comments in user_script_plug-in.sh and partnership_manager.sh
also cleaned up.

Partnership/partnership_manager.sh

@@ -1281,7 +1281,7 @@ if [[ "$MODE" == "onboard" ]]; then
         warn "DRY RUN — would write ACTIVE state and push to remote"
     fi
 
-    # Emby admin provisioning — runs after container deployment (deploy step not yet built)
+    # Emby admin provisioning — runs after container deployment
     provision_emby_admin "$MIRROR_IP"
 
     # Summary