migrate iSCSI block volumes from democratic-csi to Proxmox CSI [ci skip]

Replace TrueNAS iSCSI (democratic-csi) with Proxmox CSI plugin for all
block storage PVCs. Eliminates double-CoW (ZFS + LVM-thin) and removes
the iSCSI network hop for database I/O.

New stack: stacks/proxmox-csi/ — deploys proxmox-csi-plugin Helm chart
with StorageClass "proxmox-lvm" using existing local-lvm thin pool.

Migrated PVCs (12 total):
- Phase 1 standalone: plotting-book, novelapp, vaultwarden, nextcloud, prometheus
- Phase 2 StatefulSets: CNPG PostgreSQL (2), MySQL InnoDB (3), Redis (2)

All services verified healthy post-migration.

stacks/plotting-book/main.tf

@@ -48,12 +48,12 @@ module "tls_secret" {
 
 resource "kubernetes_persistent_volume_claim" "plotting-book-data" {
   metadata {
-    name      = "plotting-book-data"
+    name      = "plotting-book-data-proxmox"
     namespace = kubernetes_namespace.plotting-book.metadata[0].name
   }
   spec {
     access_modes       = ["ReadWriteOnce"]
-    storage_class_name = "iscsi-truenas"
+    storage_class_name = "proxmox-lvm"
     resources {
       requests = {
         storage = "1Gi"