Phase 1: API Documentation ~ Swagger

[Fastify Swagger](https://github.com/fastify/fastify-swagger) is avaiable

This is not REST friendly and will force an RPC approach. However, it also provides an excellent starting point for [Introspected REST](https://introspected.rest/) automatic generation of documentation.

Suggest starting with this and as template is uplifted to Introspected REST to add a compatible upgrade path module

The issue names Fastify Swagger and Introspected REST but no repository files, tests, or entry points. Start by reviewing the linked Fastify Swagger and Introspected REST resources, then locate the project's API documentation setup. Done means a documented Phase 1 approach and a compatible upgrade path module, with its scope agreed.

Written by the indexing model from the issue text.