Expose three tiers of components from library, ranging from high to low level

[Liampronan]

• Currently: we have a demo app that effectively acts as a full-on, drop-in solution. Move that into the library and formalize the other levels, along with documentation

// Level 1: Full solution (highest abstraction)
DualCameraScreen(mode: .pip(.front, .bottomRight))

// Level 2: View components
HStack {
    DualCameraStreamView(controller: controller, source: .back)
    DualCameraStreamView(controller: controller, source: .front)
}

// Level 3: Controller + base components
let controller = DualCameraController()
let rendererBack = controller.getRenderer(for: .back)