Adds `codegen::Html` alongside the existing `CssVariables` generator.
Walks `doc.pages[active].children` and emits absolute-positioned
`<div>` per Rect/Frame/Group + `<span>` per Text, with inline-style
position/size, RGB fill, stroke as border, corner radius (50% for
ellipses), and rotation transform. Body text is HTML-escaped.
API stays identical — both generators implement the same
`Codegen` trait, so a future CLI / Property-panel codegen
dispatcher fans out by trait object.
Tests (4 new):
- DOCTYPE + body wrapper + generator-attribution comment present
- Rect emits `<div>` with left/top/width/height + `rgb(r,g,b)` fill
- Text emits `<span>` and `&` / `<` / `>` in body get HTML-escaped
- `node.hidden = true` skipped entirely (no orphan markup)
7 generators remain to port (React + Tailwind, Vue, Svelte,
Flutter, SwiftUI, Compose, React Native) — each as a focused
follow-up commit. The trait + dispatcher shape doesn't change.
Tests total: 211 shell-core (+4) + 20 native + 8 desktop. Wasm32
build clean.
24df393c36