Extend the Open API description with the issue endpoints and regenerate the HTTP server from it

[gabor-boros]

Description

Add issue-related endpoints to the OpenAPI specification and regenerate the HTTP server code to support them.

The current OpenAPI spec lacks definitions for issue endpoints, so the HTTP server does not handle issue-related API calls yet.

Tasks

• Update the OpenAPI specification to include all issue service endpoints.
• Regenerate the HTTP server code from the updated spec (make generate.server)
• Create unimplemented (panic("not implemented")) skeleton implementation to satisfy the Strict Server interface
• Regenerate the front-end client (make generate.client)