v0.3.0

The machine draws itself: OrderFlow.to_mermaid renders the compiled
graph as Mermaid stateDiagram-v2 text.

• The shape only — the initial marker, event-labeled edges in declaration
  order (several events on one edge share a single arrow), a bare arrow
  for a direct edge — and no guards, mirroring the shape-only answer
  transitions_from gives.
• Deterministic output: repeated calls return byte-identical text, so
  golden-testing your own machines is trivial.
• The README's Introspection section shows the quick-start machine as a
  live diagram — GitHub renders mermaid fences natively — and the
  landing page's console card shows the literal output.

Full Changelog: v0.2.0...v0.3.0