Fall back to schema-root example(s) for body examples

[KeremTurgutlu]

#30 surfaces media-type-level examples/example in op docs. Some specs (e.g. Anthropic's POST /v1/messages) instead put a complete whole-payload example inside the root request schema (schema.example in 3.0, schema.examples array in 3.1) — currently dropped.

Follow-up: in _body_params, when the media type has no examples, resolve the schema and read its root example (or first of examples) as a {"default": {"value": ...}} body example. Root-level only — property-level examples are a separate issue.

Coverage scan: Anthropic 5/13 body ops have only this form (incl. /v1/messages); GitHub 10; Cloudflare 25.