CD for Proxmox — unlock VM / bare-metal / LXC / container deploys

Part of the **Continuous Delivery Vision** ([#8](https://github.com/ChrisonSimtian/Fallout/milestone/8)); tracked under **CD: Proxmox & on-prem** (#17). Chris is actively prototyping this.

## Idea

CD for **Proxmox** — which in extension unlocks deploying into **VMs** (and other regular on-prem / bare-metal machines) as well as **LXCs** and **containers**. The non-cloud target class for Fallout CD.

## Why it's a strong target

- Self-hostable (Proxmox VE nests in a VM) → cheap to exercise, no cloud bill.
- Covers a target spectrum public clouds don't: bare metal, long-lived VMs, system containers (LXC), app containers.

## Rough scope (TBD — Chris driving)

- [ ] Proxmox API integration surface (auth, node/VM/LXC lifecycle).
- [ ] Deploy primitives: provision/start/stop VM & LXC; push + run an app/container onto a target.
- [ ] Reconcile with the generic on-prem / bare-metal deploy story (SSH-based? see #250 Fallout.Ssh).
- [ ] Decide what's a first-party primitive vs. sample.

Long-horizon, no release commitment.