* refactor(design-jsx): extract design JSX into its own package
Design JSX elements, helpers, schema, reference, and JSX export only need
the scene graph, yet lived in Core, so every consumer of the authoring API
pulled in the renderer, layout, and file formats.
@open-pencil/design-jsx now owns them and depends only on scene-graph. The
renderer takes icon lookup, SVG conversion, vector creation, and layout as
DesignJSXServices; Core binds its own and exports the bound renderJSX and
renderTree from @open-pencil/core/design-jsx.
* feat(design-jsx): export the JSX runtime for TSX authoring
The package already had a JSX runtime, but nothing exported it, so design
trees could only be written as function calls or JSX strings. Export
`./jsx-runtime` and `./jsx-dev-runtime` so `jsxImportSource` works, and make
`Fragment` produce the same empty-type node as `<>` in `renderJSX` strings.
* fix(design-jsx): render fragments nested in other elements
A fragment builds a node with an empty type, which only renderJSX expanded, and only at the root. Nested fragments and fragments passed to renderTree failed with 'Unknown element: <>'. Inline fragment children when trees are built, and share root expansion between renderTree and renderJSX.
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