docs: capture PD future-state architecture

docs/architecture/HARDWARE_INVENTORY.md

@@ -47,6 +47,18 @@
 ### NFS Mounts
 - Serenity data array → `/mnt/unraid/data`
 
+### Planned PD upgrade target
+- **Platform:** HL15 Beast ASRock build (`ASRock ROMED8-2T`)
+- **Recommended CPU floor:** EPYC 7282
+- **Preferred long-term CPU:** EPYC 7452 if budget allows
+- **RAM floor:** 64GB
+- **Preferred RAM if hosting production plus multiple cyber VMs:** 128GB
+- **PSU guidance:** keep the RM1000x unless a 4090-class GPU is likely; move to HX1500i when the 4090 plan becomes real
+- **Planned storage growth:**
+  - adopt Serenity's storage role into PD
+  - add a second HDD-backed ZFS pool using 5-6 new 20TB+ drives
+  - add SSD/NVMe tiers for apps, databases, VM disks, scratch, and model cache
+
 ---
 
 ## N.O.M.A.D. (Offline Knowledge + Game Servers)