feat: proxmox import diagnostics, node style fix, and cluster edges

Scan History:
- Proxmox is now a first-class scan kind (badge, filter chip, Server icon,
  completion toast) instead of being mislabeled as an IP scan.
- A done run carrying a non-fatal advisory renders amber (info) with a
  warning toast, distinct from red failures.

Import diagnostics:
- test-connection probes /access/permissions and warns when the API token
  has no ACL (VMs/LXC would be invisible) — points at the PVEAuditor grant.
- import surfaces an advisory when hosts import but no guests are visible
  (privilege-separated token whose rights are the intersection with the user),
  rather than a silent "done".

Node style:
- Proxmox container mode is now opt-in (container_mode === true), matching the
  rest of the codebase (App.tsx nesting logic). Imported proxmox nodes leave
  the flag unset and render like a manually-created node instead of an empty
  group container.

Cluster edges:
- Hosts from one import are chained with 'cluster' edges via left/right handles,
  distinct from the vertical host->guest 'virtual' edges. Wired for both the
  direct "Add to Canvas" path and the pending -> approve path (host<->host
  proxmox_cluster links, resolved to cluster edges on approve; cluster hosts
  get left/right handles).

Tests added on both sides.

ha-relevant: maybe

frontend/src/App.tsx

@@ -47,6 +47,7 @@ import type { NodeData, EdgeData, CustomStyleDef, FloorMapConfig, NodeType } fro
 import type { ZigbeeNode, ZigbeeEdge } from '@/components/zigbee/types'
 import type { ZwaveNode, ZwaveEdge } from '@/components/zwave/types'
 import type { ProxmoxNode, ProxmoxEdge } from '@/components/proxmox/types'
+import { buildProxmoxClusterEdges } from '@/components/proxmox/clusterEdges'
 
 const STANDALONE = import.meta.env.VITE_STANDALONE === 'true'
 
@@ -650,10 +651,16 @@ export default function App() {
     const cols = Math.min(COLS, pmNodes.length)
     const rows = Math.ceil(pmNodes.length / COLS)
     const origin = getCenteredPosition(cols * SPACING_X, rows * SPACING_Y)
+    // Multiple hosts from one import = a cluster → chain them via left/right
+    // 'cluster' edges. Those endpoints need one left + one right handle each
+    // (both default to 0), so grant them to the host nodes up front.
+    const clusterEdges = buildProxmoxClusterEdges(pmNodes)
+    const cluster = clusterEdges.length > 0
     pmNodes.forEach((pn, i) => {
       const col = i % COLS
       const row = Math.floor(i / COLS)
       const position = { x: origin.x + col * SPACING_X, y: origin.y + row * SPACING_Y }
+      const isClusterHost = cluster && pn.type === 'proxmox'
       const newNode: import('@xyflow/react').Node<NodeData> = {
         id: pn.id,
         type: pn.type,
@@ -665,6 +672,7 @@ export default function App() {
           services: [],
           ...(pn.ip ? { ip: pn.ip } : {}),
           ...(pn.hostname ? { hostname: pn.hostname } : {}),
+          ...(isClusterHost ? { left_handles: 1, right_handles: 1 } : {}),
         },
       }
       addNode(newNode)
@@ -679,6 +687,16 @@ export default function App() {
         type: 'virtual',
       } as unknown as import('@xyflow/react').Connection)
     })
+    // Host ↔ host links render as 'cluster' edges (left → right chain).
+    clusterEdges.forEach((ce) => {
+      onConnect({
+        source: ce.source,
+        sourceHandle: ce.sourceHandle,
+        target: ce.target,
+        targetHandle: ce.targetHandle,
+        type: 'cluster',
+      } as unknown as import('@xyflow/react').Connection)
+    })
     const importedIds = new Set(pmNodes.map((pn) => pn.id))
     useCanvasStore.setState((state) => ({
       nodes: state.nodes.map((n) => ({ ...n, selected: importedIds.has(n.id) })),