v0.13.0

Minor Changes

• aeedcc0 Thanks @davidkpiano! - Add semantic graph validation via validateGraph(), covering shape plus graph
  invariants such as duplicate ids, dangling edges, missing parents, invalid
  initial nodes, duplicate ports, invalid port references, and parent cycles.

  Default missing graph, node, edge, and port data values to null when
  creating resolved graph objects.

  Refresh format fidelity claims and conformance tests for ELK, xyflow, and
  Mermaid state round-tripping, and expand algorithm benchmarks across sparse,
  dense, compound, multi-edge, and port-heavy graphs.