Refactor openapiMiddleware to accept multiple documents

[Copilot]

Summary

Changes openapiMiddleware from (path, url) to an array of { path, baseUrl, id? } descriptors, enabling future multi-spec support. Single-entry arrays preserve the existing /counterfact/openapi behavior; multi-entry arrays serve each spec at /counterfact/openapi/{id}.

// Before
openapiMiddleware(config.openApiPath, `//localhost:${port}${prefix}`)

// After
openapiMiddleware([{ path: config.openApiPath, baseUrl: `//localhost:${port}${prefix}` }])

For now the call site always passes a single-item array (with id omitted).

Original Prompt

Change the signature to accept an array of objects with path, baseUrl, and id. All keys are strings.

If the array has length 1, it should respond to "/counterfact/openapi" as it does now.

Otherwise, it should respond to each of /counterfact/openapi/{id}.

For now, it will always be called with an array of 1 item and the id will be undefined.

Manual acceptance tests

• GET /counterfact/openapi returns 200 with the OpenAPI YAML when a single spec is configured
• Swagger UI at /counterfact/swagger still loads correctly with a single spec
• When two descriptors are provided, GET /counterfact/openapi/spec-a and /counterfact/openapi/spec-b each return the correct spec
• When two descriptors are provided, GET /counterfact/openapi falls through (no 200)
• Each multi-doc response injects the correct servers[0].url for its own baseUrl
• Routes unrelated to /counterfact/openapi are unaffected

Tasks

• Exported OpenApiDocumentConfig interface (path, baseUrl, id?) from openapi-middleware.ts
• Refactored openapiMiddleware to accept OpenApiDocumentConfig[]; single-entry → /counterfact/openapi, multi-entry → /counterfact/openapi/{id}
• Updated create-koa-app.ts call site to pass a single-item array
• Updated existing tests and added three new tests covering multi-document routing and per-doc baseUrl injection