docs: document multi-version API support

[Copilot]

Multi-version API support had no user-facing documentation — users couldn't discover the feature or know how to configure it. This PR adds the missing docs across four areas.

Summary

New feature page — docs/features/multiple-versions.md

• YAML config syntax (group + version fields), with a field reference table marking both as required
• URL layout: how /<group>/<version>/... prefixes are derived
• Annotated generated code layout: shared routes/, shared types/paths/, per-version types/<version>/, and types/versions.ts
• Route handler authoring with $.version and $.minVersion() (generic "catalog" example, not tied to any real API)
• REPL: grouped context/routes access
• TypeScript narrowing details (Versioned<T,V> and minVersion() as a type predicate) moved to the bottom of the page for readers who want to understand the underlying types

docs/usage.md — added "Multiple versions" row to the features table.

docs/reference.md — new "Multiple API versions" section documenting SpecConfig.version, Versioned<T,V>, Versions, VersionsGTE, and types/versions.ts exports.

src/typescript-generator/versions-ts-generator.ts — added JSDoc to the generated Versions, VersionsGTE, and Versioned types so IDE tooltips are populated in the generated output file.

Original Prompt

Add user-facing documentation that explains how to configure and use multi-version API support: YAML config syntax, generated code layout, the Versioned type, route-handler authoring patterns, and REPL usage.

Multi-version support introduces several new concepts that need clear documentation for users:

• How to declare multiple versions of the same API group in the config
• The URL layout produced by the server (/<group>/<version>/...)
• The generated code layout (types/<version>/..., shared types/paths/..., types/versions.ts)
• How to write a route handler that serves multiple versions using the Versioned type
• How the REPL addresses versioned context, routes, and scenarios

Manual acceptance tests

• docs/features/multiple-versions.md exists and covers YAML config, URL layout, generated code layout, $.minVersion() handler example, and REPL usage
• The handler example in the feature page uses a generic API (not Petstore or any specific real-world API)
• docs/usage.md features table contains a "Multiple versions" row linking to ./features/multiple-versions.md
• docs/reference.md "Multiple API versions" section documents SpecConfig.version, Versioned<T,V>, Versions, VersionsGTE, and types/versions.ts
• Generating types/versions.ts for a versioned group produces Versions, VersionsGTE, and Versioned types with JSDoc comments visible in IDE hover tooltips
• All existing versions-ts-generator tests pass

Tasks

• Created docs/features/multiple-versions.md with config syntax, URL/code layout, handler authoring, and REPL sections; TypeScript narrowing details placed at the bottom
• Marked version as required in the config field reference table
• Removed the scenario-scripts-with-groups subsection (groups are orthogonal to versions)
• Added "Multiple versions" row to the features table in docs/usage.md
• Added "Multiple API versions" reference section to docs/reference.md
• Added JSDoc to Versions, VersionsGTE, and Versioned in versions-ts-generator.ts

[pmcelhaney]

Move all information about types to the bottom of multiple-versions.md. Users don't need to know how the sausage is made, but leave it at the bottom in case they're interested.

Remove the section about using scenarios with groups, as groups are orthogonal to versions.

[pmcelhaney]

version is required

[Copilot]

Fixed in da29251 — changed version from no to yes in the field table.

[Copilot]

Move all information about types to the bottom of multiple-versions.md. Users don't need to know how the sausage is made, but leave it at the bottom in case they're interested.

Remove the section abo...

Done in da29251. Moved the "TypeScript narrowing with Versioned" and "The Versioned type" content to the bottom (after REPL usage). Also removed the "Running scenario scripts for a versioned group" subsection from the REPL section.