Add the Cratis sample learning roster

[woksin]

Summary

Creates a discoverable, buildable sample learning path across Chronicle, Arc + React, multi-tenancy, cross-store messaging, operations, model-first development, and the Library showcase.

Added

• Add focused Chronicle backend, processing, multi-tenant, cross-store, and operations samples.
• Add the Idea Loom Arc + React sample with generated contracts and Cratis Components.
• Add a bounded Screenplay and Stage model-first Library sample.
• Add a machine-readable sample catalog with validation and polished developer guides.

Changed

• Align the Samples solution, frontend workspaces, CI, dependency setup, and Library showcase with the active roster.

Removed

• Remove the incompatible legacy Terminal.Gui console quickstart from the active sample path.