Implement MintPlayer.AspNetCore.Endpoints library

[PieterjanDeClippel]

Summary

• Implements the class-per-endpoint mapping library as designed in the PRD (Add PRD for MintPlayer.AspNetCore.Endpoints library #26)
• Abstractions: IEndpointBase, IEndpoint, IEndpoint<T>, IEndpoint<T,R>, convenience interfaces (GET/POST/PUT/DELETE/PATCH × 3 variants), IEndpointGroup + IMemberOf<TGroup>, attributes, EndpointDescriptor
• Runtime: Abstract base class hierarchy — BodyEndpoint<T> with MVC input formatter content negotiation + JSON fallback, NonBodyEndpoint<T> with forced explicit binding, MapEndpoint<T>() manual registration
• Generator: IIncrementalGenerator that discovers endpoints, generates partial class base declarations and MapXxxEndpoints() extension with factory caching, try/finally disposal, attribute transfer, route groups, and .Produces<TResponse>() for OpenAPI

Key design points

• Static abstract interface members for compile-time route enforcement (no instance at startup)
• Partial class trick: user writes partial class X : IPostEndpoint<T>, generator adds partial class X : PostEndpoint<T>
• Generic helpers in generated code to access static abstract members through constraints
• Content negotiation transparent to endpoint (JSON/XML/custom via MVC formatters)
• Diagnostics: MPEP001 (non-partial), MPEP002 (base class conflict), MPEP003 (multiple groups)

Test plan

• Build passes for all three projects (verified locally)
• Full solution build succeeds with no new warnings
• Create a sample app to validate source generator output (Phase 3)
• Verify partial class generation, mapping extension, content negotiation, disposal, groups, attributes

🤖 Generated with Claude Code