docs: add migration checklist for new GTHost Detroit server

SCRATCH/migration-new-host.md

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+# Migration Checklist — New GTHost Detroit Server
+
+**New hardware:** Supermicro 2029TP-HTR, Intel Gold 6152 22c/44t, 192GB DDR4, 2x1.92TB SSD  
+**Target OS:** Proxmox 9 (fallback: Proxmox 8 if issues)  
+**Old server:** Denver, Silver 4116, $103/mo → cancel after migration confirmed
+
+---
+
+## Pre-Migration
+
+- [ ] Verify PBS backup is current and all VMs/containers have recent backups
+- [ ] Note all VM IDs and names from current Proxmox
+- [ ] Note VLAN/bridge config from current OPNsense setup
+- [ ] Export OPNsense config (both routers) — System → Configuration → Backups
+
+---
+
+## Phase 1 — New Server Setup (est. 2-4 hrs)
+
+- [ ] GTHost provisions server (5-15 mins)
+- [ ] Install Proxmox 9 via GTHost panel
+- [ ] Initial Proxmox config:
+  - [ ] Set hostname
+  - [ ] Configure network bridges to match current layout
+  - [ ] Set up VLANs
+- [ ] Add new server as additional node or standalone in PBS
+- [ ] Verify PBS can see backup repository
+
+---
+
+## Phase 2 — Restore VMs (est. 2-4 hrs)
+
+Restore in this order — networking first:
+
+- [ ] OPNsense core router (VM)
+- [ ] OPNsense zpack router (VM)
+- [ ] zlh-dns (Technitium)
+- [ ] zlh-proxy (Traefik core)
+- [ ] zlh-zpack-proxy (Traefik game/dev edge)
+- [ ] zlh-monitor (Prometheus/Grafana)
+- [ ] zlh-artifacts
+- [ ] zpack-api
+- [ ] zpack-portal
+- [ ] zlh-velocity (Minecraft proxy)
+- [ ] zlh-back (PBS — if moving)
+- [ ] Game/dev containers
+
+---
+
+## Phase 3 — Verification (est. 2-4 hrs)
+
+- [ ] Internal networking between VMs working
+- [ ] Portal loads
+- [ ] API responds
+- [ ] Twingate connector online — update connector to new server if needed
+- [ ] Dev container provisions and browser IDE loads
+- [ ] Game server provisions and Minecraft connects via Velocity
+- [ ] PBS backup runs successfully on new host
+- [ ] Monitoring shows all services
+
+---
+
+## Phase 4 — DNS Cutover (est. 30 mins)
+
+- [ ] Update Cloudflare A record for Velocity public IP
+- [ ] Update Cloudflare SRV records for Minecraft
+- [ ] Update any other DNS records pointing to old server IPs
+- [ ] Monitor for issues — 30 min observation window
+- [ ] Confirm everything stable
+
+---
+
+## Phase 5 — Cleanup
+
+- [ ] Cancel old Denver server (or let expire)
+- [ ] Update PROJECT_CONTEXT.md with new VM map and IPs
+- [ ] Update OPEN_THREADS.md — mark migration complete
+
+---
+
+## Notes
+
+- Everything runs on private IPs internally — no hardcoded public IP dependencies
+- DNS cutover is the only external change
+- Worst case: reinstall Proxmox 8 and repeat
+- IPMI available via GTHost panel for out-of-band access if needed
+- Proxmox 9 ships with kernel 6.14, LXC 6.0 — no API changes required