feat(admin): import existing host VMs (#166)

[v0l]

Fixes #166

Summary

Adds an admin capability to adopt VMs that already exist on a host but aren't tracked in the database.

• GET /api/admin/v1/hosts/{id}/vms/unmanaged — lists host VMs with no matching DB record (host vmid, mapped DB id, name, CPU/memory/disk specs, storage, MAC, running state).
• POST /api/admin/v1/hosts/{id}/vms/import ({ host_vm_id, user_id, reason? }) — imports one VM: assigned to user_id and billed via the region's custom pricing (required — fails if the region has none), capturing the VM's current CPU/memory/disk specs into a custom template. Returns a job_id. Proxmox only.

Architecture

The admin service has no direct host connection (host actions go through the worker over Redis), so both operations dispatch a WorkJob to the worker. Per design, discovery replies over a temporary Redis pub/sub channel (per-request UUID) reusing the existing job-feedback infra — the admin endpoint subscribes before dispatching and waits (30s timeout) for the Completed { result } payload.

Imported VMs use the fixed Proxmox id mapping (vmid = db_id + 100), inserted via a new insert_vm_with_id, so all subsequent lifecycle operations target the correct host VM.

Changes

• lnvps_db / mock: insert_vm_with_id (explicit-id insert)
• lnvps_api_common: shared HostVmSpec type; ListUnmanagedVms + ImportVm work jobs
• lnvps_api: VmHostClient::list_host_vms trait method + Proxmox impl (net0/scsi0 parsing, ProxmoxVmId::inner), VmProvisioner::import_vm, worker handlers, DummyVmHost discovery registry for tests
• lnvps_api_admin: two endpoints + request/response models
• API_CHANGELOG.md

Tests

• test_import_vm — success, re-import rejection, not-found, missing-custom-pricing scenarios
• parse_mac_from_net, parse_storage_from_disk, proxmox_vm_id_inner
• Workspace builds, fmt clean, no new clippy issues; affected crate test suites pass.

Notes / follow-ups

• IP assignments are not imported yet (specs = CPU/mem/disk only); can be added later.
• Imported VMs get a placeholder OS image (required FK) since the real OS is unknown — cosmetic, only used on reinstall.