Add new skill documentation files for developing OECS, testing games,
and writing games. Also update the API surface documentation to include
guidance on component and command definitions.
Update the API surface and implementation plan to reflect architectural
changes, including new iterator overloads, system design refinements,
and the introduction of a source generator.
Initializes the OECS repository with the core foundation, including:
- Entity management with 24-bit IDs and 8-bit versioning
- Sparse set-based component storage
- Entity allocation and recycling logic
- Core World API for entity and component lifecycle
- Project scaffolding for source and unit tests
- Design documentation and architecture decision records (ADRs)