Schema generics and parameterized helpers

[Romakita]

Objective

Introduce patterns for defining generic schemas (e.g., paged responses) with strong type inference, including inference for nested generics.

Details

• Document and implement helpers like makePaged<T>(item: JsonSchema<T>).
• Ensure nested generics are handled correctly in both runtime and type inference.
• Provide migration and usage documentation.

Parent Epic: schema-inference-epic