Add Scalar and Swagger UI Endpoints for OpenAPI Docs

[jaypatrick]

Expose API docs at both /api/docs (Scalar) and /api/swagger (Swagger UI):

• Add Scalar (@scalar/hono-api-reference) for modern OpenAPI UI
• Add Swagger UI (@hono/swagger-ui) for compatibility
• Both to consume /api/openapi.json
• Document both in API overview

Reference:

• https://hono.dev/examples/scalar/
• https://hono.dev/examples/swagger-ui/

[github-actions]

The GitHub issue proposes adding two new endpoints, /api/docs and /api/swagger, to serve OpenAPI documentation for an API. The /api/docs endpoint will utilize Scalar (@scalar/hono-api-reference) for a modern, streamlined OpenAPI UI, while the /api/swagger endpoint will rely on Swagger UI (@hono/swagger-ui) for broader compatibility. Both interfaces will retrieve their data from a single OpenAPI specification file located at /api/openapi.json. Additionally, the issue calls for updating the API overview documentation to include details about both endpoints. Links to Scalar and Swagger UI examples are provided for reference.