Add docs for AcBinary MVC formatters and pipeline updates
Comprehensive documentation for new ASP.NET Core MVC formatters supporting AcBinary, including registration, media type, request/response flow, error handling, and future plans. Updated project and topic docs to reference MVC formatters and folder structure. Added performance planning entry for StreamPipeWriter congestion fallback. Expanded markerless schema lane rationale and updated architecture docs to reflect MVC formatter integration. Improved navigation and layering documentation.
