docs: lock in storage philosophy and PDM migration capability

Storage philosophy (user directive):
- NVMe/SSD: k8s worker scratch + ultix-streaming (dev workstation
  running "cluster of 1" pre-prod jobs before full k8s deployment)
- Spinning rust: all infrastructure VMs (UCS, netinfra, LibreNMS, SIEM)

Clarified that hosts are standalone but managed via Proxmox Datacenter
Manager (PDM), which supports VM migration between nodes through the
UI -- eliminating the need for manual disk copies in the migration plan.

Updated all migration steps to reference PDM storage migrate instead
of manual cp commands.

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Assisted-by: Crush:glm-5.2

AGENTS.md

@@ -112,9 +112,13 @@ use `deploy-check.sh` / `deploy-tuning.sh` wrapper patterns instead.
    `/etc/network/interfaces` with awk (sed fails on tab-indented stanza).
 4. Always shellcheck before shipping: `docker run --rm -v "$PWD:/mnt"
    koalaman/shellcheck:stable --severity=style scripts/*.sh`
-5. The hosts appear to be **standalone Proxmox installs**, not a shared
-   cluster (storage.cfg differs per host). VMs are pinned to their host.
-   Moving VMs requires manual disk migration, not live migration.
+5. The hosts are **standalone Proxmox installs** (not a pvecm cluster), but
+   managed collectively via **Proxmox Datacenter Manager (PDM)**. PDM supports
+   VM migration between nodes via the UI. NFS exports are visible to all nodes;
+   local storage migration is done through PDM's "Storage Migrate" function.
+6. **Storage philosophy:** NVMe/SSD is for k8s worker scratch + ultix-streaming
+   (developer workstation for "cluster of 1" pre-prod jobs). Spinning rust
+   hosts all infrastructure VMs (UCS, netinfra, LibreNMS, SIEM).
 
 ## Friday walkthrough (user action)