Native (JSON) render-target backend.

Emits the byte sequences that make up the s statics as a JSON widget tree for native clients (iOS/SwiftUI, Android/Compose, ...). Each element becomes a flat JSON object:

{"type": "Column", "az": "0", "padding": "16", "children": [ ... ]}

type, az and children are reserved keys; every other key is a widget prop. The framework is vocabulary-agnostic -- the tag atom is emitted verbatim as type and the client engine maps it to a real widget. Dynamic text children become addressable #text nodes so the diff engine can target them by az.

String keys and values are escaped via json:encode/1, so the zipped statics form valid JSON. So do the dynamics in the zipped document (escape/1, render_attr/2): a scalar is a JSON string, an effect command its array and a typed boolean prop a JSON boolean, exactly what a client builds by JSON-encoding the wire value. On the wire itself a value stays raw (wire_escape/1, wire_attr/2), because the client does that encoding.