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

mcp/app/tools.py

@@ -24,11 +24,12 @@ def register_tools(server: Server):
                 "type": "object",
                 "required": ["id"],
                 "properties": {
-                    "id":       {"type": "string"},
-                    "label":    {"type": "string"},
-                    "ip":       {"type": "string"},
-                    "hostname": {"type": "string"},
-                    "status":   {"type": "string"},
+                    "id":        {"type": "string"},
+                    "label":     {"type": "string"},
+                    "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"})