Add @openuidev/svelte-lang and extract @openuidev/lang-core

[shipooor]

Closes #302

What

Adds @openuidev/svelte-lang — a Svelte 5 renderer for OpenUI Lang — and extracts the framework-agnostic core into @openuidev/lang-core, as suggested by @AbhinRustagi in this comment.

Architecture

@openuidev/lang-core          (parser, prompt, validation, generic Library<C>)
       ↑              ↑
@openuidev/react-lang    @openuidev/svelte-lang
  (thin React wrapper)     (thin Svelte 5 wrapper)

• lang-core holds all framework-agnostic code: parser, prompt generation, validation, and a generic Library<C> / DefinedComponent<T, C> system where C is the framework component type.
• react-lang narrows C to React.FC and re-exports everything. Public API is unchanged — this is a transparent refactor.
• svelte-lang narrows C to Component<Props> and implements the Svelte 5 rendering layer.

This structure makes adding future framework adapters (Vue, Solid, etc.) straightforward.

Changes

1. @openuidev/lang-core (new package)

• Parser (createParser, createStreamingParser) moved from react-lang
• Prompt generation (generatePrompt) moved from react-lang
• Validation (validate, parseRules, builtInValidators) moved from react-lang
• Generic Library<C> and DefinedComponent<T, C> types

2. @openuidev/react-lang (refactored, no API change)

• Imports parser/prompt/validation from lang-core instead of local files
• library.ts is now a thin wrapper that narrows C to React.FC
• All public exports remain identical

3. @openuidev/svelte-lang (new package)

• Renderer.svelte — streaming renderer using $derived for reactive parsing
• RenderNode.svelte — recursive component renderer with <svelte:boundary> error handling
• library.ts — defineComponent / createLibrary with Svelte 5 types
• context.svelte.ts — context API (getOpenUIContext, getTriggerAction, etc.)
• validation.svelte.ts — form validation with $state-backed reactive errors
• 30 tests (Vitest + @testing-library/svelte)

4. examples/svelte-chat (new example)

• SvelteKit app with 4 components (Stack, Card, TextContent, Button)
• Demonstrates action handling and nested component rendering

Svelte 5 features used

• $props(), $state, $derived, $effect runes
• {#snippet} / {@render} for recursive rendering (renderNode passed as snippet prop)
• <svelte:boundary> for per-component error isolation
• getContext / setContext with Symbol keys and getter pattern for reactivity

React → Svelte API mapping

React	Svelte	Notes
useOpenUI()	getOpenUIContext()	Svelte uses getContext, not hooks
useRenderNode()	snippet prop	Avoids stale closures
useTriggerAction()	getTriggerAction()
useIsStreaming()	getIsStreaming()
useState / useMemo	$state / $derived
useEffect	$effect
ErrorBoundary class	<svelte:boundary>	Shows nothing on error (no last-valid-children equivalent in Svelte)

Verification

pnpm --filter @openuidev/lang-core run build       # tsc clean
pnpm --filter @openuidev/react-lang run build       # tsc clean, API unchanged
pnpm --filter @openuidev/svelte-lang run build      # svelte-package clean
pnpm --filter @openuidev/svelte-lang run check      # svelte-check: 0 errors
pnpm --filter @openuidev/svelte-lang run test       # 30/30 tests pass
pnpm --filter svelte-chat run build                 # vite build clean
pnpm --filter openui-chat run build                 # existing example still works
pnpm --filter shadcn-chat run build                 # existing example still works

[abhithesys]

I ran the example, chat ui isn't working. At high level PR looks good. Can you update the example to use OpenAI api, while we are reviewing.

[abhithesys]

@shipooor I m making minor changes required in this PR to unblock other Renderers.