chore(storage): Longhorn over-provisioning 100->200% + right-size plex config 20->8Gi

The 39Gi/node Longhorn data disks at 1:1 over-provisioning can't fit the media stack
(plex 20Gi replica failed: 'insufficient storage'). Volumes are thin-provisioned config-only,
so 200% lets the full catalog fit without a disk resize; physical fill risk is low. Also
right-sized plex config (20Gi was excessive for metadata). Prod-grade path: grow the data
disks (WS-STORAGE follow-up).

platform/longhorn/helmrelease.yaml

@@ -62,8 +62,10 @@ spec:
       storageReservedPercentageForDefaultDisk: "20"
       # Stop scheduling new replicas onto a disk once free space drops below 25%.
       storageMinimalAvailablePercentage: "25"
-      # Dev: no thin over-provisioning — requested capacity must physically fit (1:1).
-      storageOverProvisioningPercentage: "100"
+      # Dev: 200% thin over-provisioning — config-only volumes use little actual space, so the small
+      # 39Gi data disks host the full app catalog. Physical fill risk is low (watch monitoring PVCs).
+      # Prod-grade alternative: grow the Longhorn data disks and return to 1:1 (WS-STORAGE).
+      storageOverProvisioningPercentage: "200"
 
       # --- misc dev-appropriate defaults ---
       # Keep replicas spread for durability rather than co-locating with the pod.