feat(mcp): expose parent_id in update_node tool

- Add parent_id to NodeUpdate schema in backend so PATCH /nodes/{id}
  accepts it (was silently ignored before)
- Expose parent_id in update_node MCP tool schema so the MCP SDK
  forwards it to the backend instead of stripping it
- Add regression tests in both backend and MCP layers

backend/app/schemas/nodes.py

@@ -42,6 +42,7 @@ class NodeUpdate(BaseModel):
     notes: str | None = None
     pos_x: float | None = None
     pos_y: float | None = None
+    parent_id: str | None = None
     container_mode: bool | None = None
     custom_colors: dict[str, Any] | None = None
     custom_icon: str | None = None

backend/tests/test_nodes.py

@@ -102,6 +102,16 @@ async def test_update_node_container_mode(client: AsyncClient, headers: dict):
     assert res.json()["container_mode"] is True
 
 
+async def test_update_node_parent_id(client: AsyncClient, headers: dict):
+    parent = await client.post("/api/v1/nodes", json={"type": "proxmox", "label": "PVE", "status": "unknown"}, headers=headers)
+    parent_id = parent.json()["id"]
+    child = await client.post("/api/v1/nodes", json={"type": "lxc", "label": "Child", "status": "unknown"}, headers=headers)
+    child_id = child.json()["id"]
+    res = await client.patch(f"/api/v1/nodes/{child_id}", json={"parent_id": parent_id}, headers=headers)
+    assert res.status_code == 200
+    assert res.json()["parent_id"] == parent_id
+
+
 async def test_create_node_requires_auth(client: AsyncClient):
     res = await client.post("/api/v1/nodes", json={"type": "server", "label": "N", "status": "unknown"})
     assert res.status_code == 401

mcp/app/tools.py

@@ -29,6 +29,7 @@ def register_tools(server: Server):
                     "ip":        {"type": "string"},
                     "hostname":  {"type": "string"},
                     "status":    {"type": "string"},
+                    "parent_id": {"type": "string", "description": "ID of the parent node (e.g. Proxmox host for a VM/LXC). Pass null to detach."},
                 },
             }),
             Tool(name="delete_node", description="Delete a node from the canvas", inputSchema={

mcp/tests/test_tools.py

@@ -26,6 +26,12 @@ async def test_update_node(mock_backend):
     mock_backend.patch.assert_called_once_with("/api/v1/nodes/42", {"label": "New name"})
 
 
+@pytest.mark.anyio
+async def test_update_node_parent_id(mock_backend):
+    await _dispatch("update_node", {"id": "42", "parent_id": "proxmox-1"})
+    mock_backend.patch.assert_called_once_with("/api/v1/nodes/42", {"parent_id": "proxmox-1"})
+
+
 @pytest.mark.anyio
 async def test_delete_node(mock_backend):
     await _dispatch("delete_node", {"id": "42"})