fix: NFS outage recovery — migrate to NFSv4, add alerting

NFS server restart broke NFSv3 (lockd kernel bug on PVE 6.14).
All 52 NFS PVs patched to nfsvers=4, NFSv3 disabled on PVE.

Changes:
- nfs_volume module: add nfsvers=4 mount option
- nfs-csi StorageClass: add nfsvers=4 mount option
- dbaas: MySQL serverInstances 3→1, mysql-native-password=ON
- monitoring: add NFSCSINodeDown and NFSMountFailures alerts

[ci skip]

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

modules/kubernetes/nfs_volume/main.tf

@@ -44,6 +44,7 @@ resource "kubernetes_persistent_volume" "this" {
     volume_mode                      = "Filesystem"
 
     mount_options = [
+      "nfsvers=4",
       "soft",
       "timeo=30",
       "retrans=3",