Add oold-python to the tutorial (object-graph binding examples)

[simontaurus]

Extend the tutorial to demonstrate the oold Python library, going beyond plain validation (check-json-schema-meta) and RDF generation (rdfpipe).

Focus on object-graph binding: loading OO-LD instances into typed Python objects and following references between them. Suggested examples:

• Bind an instance (e.g. jane-smith.json) to a typed Python object via its OO-LD schema.
• Resolve linked references (an entity referenced by @id, or an x-oold-range target) into connected Python objects - i.e. materialize the object graph.
• Round-trip: mutate the Python objects and serialize back to conformant OO-LD instances.
• Show how the JSON-LD @context and the x-oold-* annotations drive the binding.

Relates to OO-LD/project-management#16 (tutorial review).