Release v4.19.0

Added

• Stage accepts Screenplay's typed-context descriptors (Screenplay 4.41) alongside a model's implementation attachments. LoadedSemanticModel.TypedContextDescriptors, the matching ArtifactRenderRequest members and a new CratisRendering.Plan overload carry them from the same compilation. Stage admits descriptor contract revision 1 only, and refuses descriptors that are not ready for wrapper generation, come from another compilation, are malformed or incomplete, with STAGE-ESM-021.
• Stage generates typed C# contexts from the descriptors for validation, never falling back to dynamic. No generated code uses them yet: they are emitted once reducer bodies render. This is part of #151.

Changed

• Stage now uses Screenplay 4.41.0. Models with evolved events (ESM v4) are still refused with STAGE-ESM-016, which is now reported before any descriptor check.
• The reducer-body rejection (STAGE-ESM-019) names only what is still missing.
• Specifications attach typed event-source context for every executable-model version after v1, as Screenplay's reference evaluator does.