Replaces string-based `SpaceLayerKinds` constants with a strongly-typed `SpaceLayerKind` enum. Updates backend services, runtime models, and projection logic to use the new enum. Adds `ToContractValue` method for compatibility with existing contracts.
Adds an `.editorconfig` file with C# and project-specific conventions. Applies consistent indentation and formatting across backend handlers, runtime models, and AI services.
