feat: import hosts/VMs/LXC from Proxmox VE with optional auto-sync

Add a Proxmox VE importer that reads the /api2/json REST API with a read-only
API token and drops hosts (proxmox), VMs (vm) and LXC containers (lxc) onto the
canvas as typed nodes with run state and hardware specs (vCPU/RAM/disk).

- Backend: proxmox_service (httpx) + proxmox routes (test-connection, import,
  import-pending, config). Two-tier dedupe — merge onto an existing scanned node
  by IP, else synthetic pve-{host}-{vmid} identity. Update-in-place, never
  deletes. Host->guest rendered as a 'virtual' edge via the pending-link flow.
- Security: token is env-only (PROXMOX_TOKEN_*), never written to disk by the
  app, never returned by any endpoint; errors are credential-sanitized.
- Auto-sync: optional scheduled re-import into pending (APScheduler job).
- PendingDevice.properties carries specs through approve (+ migration).
- Frontend: ProxmoxImportModal, sidebar entry, pending inventory source filter,
  Settings auto-sync section, proxmoxApi client.
- Docs: docs/proxmox-import.md, README + FEATURES sections, .env.example keys.
- Tests: backend service/router/scheduler, frontend modal/client/pending.

ha-relevant: maybe

frontend/src/api/client.ts

@@ -120,6 +120,51 @@ export const settingsApi = {
   save: (data: AppSettings) => api.post<AppSettings>('/settings', data),
 }
 
+export interface ProxmoxConnection {
+  host: string
+  port: number
+  token_id?: string
+  token_secret?: string
+  verify_tls?: boolean
+}
+
+export interface ProxmoxConfigData {
+  host: string
+  port: number
+  verify_tls: boolean
+  sync_enabled: boolean
+  sync_interval: number
+  token_configured: boolean
+}
+
+export const proxmoxApi = {
+  testConnection: (data: ProxmoxConnection) =>
+    api.post<{ connected: boolean; message: string }>('/proxmox/test-connection', data),
+
+  importNetwork: (data: ProxmoxConnection) =>
+    api.post<{
+      nodes: import('@/components/proxmox/types').ProxmoxNode[]
+      edges: import('@/components/proxmox/types').ProxmoxEdge[]
+      device_count: number
+    }>('/proxmox/import', data),
+
+  importToPending: (data: ProxmoxConnection) =>
+    api.post<{
+      id: string
+      status: string
+      kind: string
+      ranges: string[]
+      devices_found: number
+      started_at: string
+      finished_at: string | null
+      error: string | null
+    }>('/proxmox/import-pending', data),
+
+  getConfig: () => api.get<ProxmoxConfigData>('/proxmox/config'),
+  saveConfig: (data: Omit<ProxmoxConfigData, 'token_configured'>) =>
+    api.post<ProxmoxConfigData>('/proxmox/config', data),
+}
+
 export const designsApi = {
   list: () => api.get<import('@/types').Design[]>('/designs'),
   create: (data: { name: string; icon?: string; design_type?: string }) =>