PhysicsBox. Adding physics to compose driven projects

PhysicsBox is a Kotlin library wrapping JBox2D that adds physics simulation to Jetpack Compose and Compose Multiplatform projects. The guide walks through setup via Gradle dependencies, then progressively builds a demo: adding physics bodies with `Modifier.physicsBody`, creating shapes (circles, triangles, polygons, trapezoids), configuring body properties like gravity scale, density, friction, and damping, setting up collision filters for selective object interaction, and applying impulses via `PhysicsBoxState`. Configuration of world boundaries, restitution, and gravity direction is also covered. The library targets interactive UI screens and presentations, not game development.