feat: add create_design tool so the MCP can create canvases

Wrap POST /api/v1/designs so AI clients can create a new design (canvas) and get its id back for use as design_id. Completes the create-and-target canvas workflow alongside list_designs.

Co-authored-by: Cursor <cursoragent@cursor.com>

mcp/tests/test_tools.py

@@ -249,6 +249,19 @@ async def test_list_designs(mock_backend):
     assert result == [{"id": "d1", "name": "Network Topology", "node_count": 12}]
 
 
+@pytest.mark.anyio
+async def test_create_design(mock_backend):
+    mock_backend.post = AsyncMock(return_value={"id": "d2", "name": "Scan Devices"})
+    result = await _dispatch("create_design", {"name": "Scan Devices"})
+    mock_backend.post.assert_called_once_with("/api/v1/designs", {"name": "Scan Devices"})
+    assert result == {"id": "d2", "name": "Scan Devices"}
+
+
+def test_create_design_schema_requires_name():
+    tool = next(t for t in TOOLS if t.name == "create_design")
+    assert tool.inputSchema["required"] == ["name"]
+
+
 @pytest.mark.anyio
 async def test_unknown_tool():
     with pytest.raises(ValueError, match="Unknown tool"):