feat(api): Add LXC snapshot routes

[pparage]

Context

The proxmox_controller role supports LXC snapshots (snapshot_lxc_create, snapshot_lxc_delete, snapshot_lxc_revert, snapshot_lxc_list) but these are not exposed via API routes.

Requirements

• POST /v0/admin/proxmox/lxc/{id}/snapshot/create
• DELETE /v0/admin/proxmox/lxc/{id}/snapshot/delete
• POST /v0/admin/proxmox/lxc/{id}/snapshot/revert
• GET /v0/admin/proxmox/lxc/{id}/snapshot/list
• Pydantic schemas for each

Priority

Important. Should be implemented alongside B4 (LXC lifecycle routes).

References

• Gap analysis: gap-analysis.md issue B9

[pparage]

Implemented in #99 (feature/v1-proxmox-readops).

Per-VM snapshot routes are now available under v1, supporting both qemu and lxc via ?vmtype=:

• GET /v1/proxmox/hosts/{host_id}/vms/{vmid}/snapshots → Page[SnapshotItem] (filters PVE's synthetic current)
• POST /v1/proxmox/hosts/{host_id}/vms/{vmid}/snapshots (create) → UPID
• DELETE /v1/proxmox/hosts/{host_id}/vms/{vmid}/snapshots/{name} → UPID
• POST /v1/proxmox/hosts/{host_id}/vms/{vmid}/snapshots/{name}/rollback → UPID (vmid-guarded)

Approach is direct PVE httpx (consistent with the existing v1 vms.py/hosts.py), not the v0 Ansible path. The qemu-only vmstate flag is omitted for LXC, matching community.proxmox proxmox_snap.

Leaving this open until #99 merges into dev.