arrstack,fafflix,cheeztv: provision shared mediastore CephFS volume

Adds the static PV/PVC trio for the new 10Ti "mediastore" CephFS subvolume
plus a bootstrap Job that seeds its directory tree. Purely additive: the
existing media-tv/media-movies volumes are untouched.

- add static PVs arrstack-mediastore, fafflix-mediastore, cheeztv-mediastore
  all pinned to the same rootPath on cephfs_csi_ssd_ec_4_1
- add the matching RWX 10Ti PVCs, k8up-excluded, statically bound by
  volumeName + storageClassName ""
- add mediastore-bootstrap, an ArgoCD Sync-hook Job that mkdir -p's
  /{fafflix,cheeztv}/{tvseries,movies} and /nzbget/downloads/complete as
  uid/gid 1000
- wire the new manifests into the arrstack, fafflix and cheeztv bases

apps/base/arrstack/pv-mediastore.yaml

@@ -0,0 +1,32 @@
+---
+# Static PV for the shared MEDIASTORE CephFS subvolume: one 10Ti filesystem
+# holding every library plus the nzbget download tree, so arr imports are
+# same-filesystem hardlink moves across tv AND movies. Same rootPath as the
+# fafflix/cheeztv mediastore PVs; each namespace gets its own PV (unique name +
+# volumeHandle) pinned by claimRef.
+apiVersion: v1
+kind: PersistentVolume
+metadata:
+  name: arrstack-mediastore
+spec:
+  capacity:
+    storage: 10Ti
+  accessModes:
+    - ReadWriteMany
+  persistentVolumeReclaimPolicy: Retain
+  storageClassName: ""
+  volumeMode: Filesystem
+  claimRef:
+    namespace: arrstack
+    name: mediastore
+  csi:
+    driver: cephfs.csi.ceph.com
+    volumeHandle: arrstack-mediastore-static
+    nodeStageSecretRef:
+      name: csi-cephfs-secret
+      namespace: csi-cephfs
+    volumeAttributes:
+      staticVolume: "true"
+      clusterID: cephfs_csi_ssd_ec_4_1
+      fsName: cephfs
+      rootPath: /volumes/csi_ssd_ec_4_1/mediastore/a0152dac-a51b-4b95-ac5e-ecdd99bfe3f1