guacamole: add volumeMode to guac-mysql PVC template

Closes the infra-guacamole OutOfSync sync loop. K8s API sets
volumeMode=Filesystem as a default on volumeClaimTemplates at creation,
but the git manifest omitted it. ArgoCD uses ServerSideApply with
atomic ownership of volumeClaimTemplates, so every sync saw a
desired/live mismatch on that one field. volumeClaimTemplates is
immutable after creation so ArgoCD could never reconcile it --
autoHealAttemptsCount climbed to 6091. Adding the field to git
matches live and breaks the loop.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/guacamole/guacamole.yaml

@@ -90,6 +90,7 @@ spec:
         name: guac-mysql-data
       spec:
         accessModes: [ReadWriteOnce]
+        volumeMode: Filesystem
         resources:
           requests:
             storage: 5Gi