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

backend/app/services/proxmox_service.py

@@ -192,6 +192,21 @@ def build_proxmox_properties(node: dict[str, Any]) -> list[dict[str, Any]]:
     return props
 
 
+def build_proxmox_cluster_links(nodes: list[dict[str, Any]]) -> list[tuple[str, str]]:
+    """Chain host nodes (``type == 'proxmox'``) into cluster links.
+
+    Hosts from one import belong to the same cluster, so they are linked
+    host↔host (rendered as ``cluster`` edges via left/right handles, distinct
+    from the vertical host→guest ``virtual`` edges). Returns consecutive
+    ``(source_ieee, target_ieee)`` pairs, or ``[]`` for a single host. Mirrors
+    the frontend ``buildProxmoxClusterEdges``.
+    """
+    hosts = [n["ieee_address"] for n in nodes if n.get("type") == "proxmox" and n.get("ieee_address")]
+    if len(hosts) < 2:
+        return []
+    return [(hosts[i], hosts[i + 1]) for i in range(len(hosts) - 1)]
+
+
 def _parse_inventory(
     hosts_raw: list[dict[str, Any]],
     guests_by_host: dict[str, list[dict[str, Any]]],
@@ -231,6 +246,23 @@ async def _get_json(client: httpx.AsyncClient, path: str) -> Any:
     return resp.json().get("data")
 
 
+async def _token_has_permissions(client: httpx.AsyncClient) -> bool:
+    """True if the API token holds *any* ACL.
+
+    Proxmox list endpoints (``/qemu``, ``/lxc``) silently return an empty
+    ``200`` when the token lacks ``VM.Audit`` — indistinguishable from a host
+    that genuinely has no guests. ``GET /access/permissions`` returns ``{}`` for
+    a token with no ACL at all, which is the common misconfiguration (a
+    privilege-separated token created without its own permission). Best-effort:
+    on any error assume permissions exist so we never block a valid import.
+    """
+    try:
+        perms = await _get_json(client, "/access/permissions")
+    except httpx.HTTPError:
+        return True
+    return bool(perms) if isinstance(perms, dict) else True
+
+
 async def fetch_proxmox_inventory(
     host: str,
     port: int,
@@ -339,8 +371,16 @@ async def test_proxmox_connection(
             timeout=timeout,
         ) as client:
             data = await _get_json(client, "/version")
+            has_perms = await _token_has_permissions(client)
         version = (data or {}).get("version", "?") if isinstance(data, dict) else "?"
-        return True, f"Connected to Proxmox VE {version}"
+        message = f"Connected to Proxmox VE {version}"
+        if not has_perms:
+            message += (
+                " — warning: this API token has no permissions, so VMs and LXC "
+                "will not be visible. Assign the PVEAuditor role at path '/' to the "
+                "token in Proxmox (Datacenter → Permissions → API Token Permission)."
+            )
+        return True, message
     except httpx.HTTPError as exc:
         return False, _sanitize_proxmox_error(exc)
     except Exception as exc:  # noqa: BLE001 — surface a safe message, log the rest