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).

catalog/plex.yaml

@@ -27,7 +27,7 @@ exposure: public              # edge port-forward + public DNS; clients + Seerr
 egress: internet              # normal WAN egress (docs/03; R-NET-05)
 storage:
   - name: config
-    size: 20Gi
+    size: 8Gi
     class: longhorn           # Plex DB/metadata: replicated app state on the 3-replica tier (docs/04; R-STATE-01/02)
 dependencies: []              # default-deny: reaches only DNS; clients/Seerr reach IT (docs/03; R-NET-01/02)
 ingressRoutes: