- Convert BlueprintComponent from interface to actual ECS Component class
- Add ready-to-use BlueprintSystem that extends EntitySystem
- Remove deprecated legacy APIs (createBlueprintSystem, etc.)
- Update all blueprint documentation (Chinese & English)
- Simplify user API: just add BlueprintSystem and BlueprintComponent
BREAKING CHANGE: BlueprintComponent is now a class extending Component,
not an interface. Use `new BlueprintComponent()` instead of
`createBlueprintComponentData()`.