refactor(react)!: delete the React basic catalog implementation

[josemontespg]

The v0_9 React renderer renders the basic catalog through the Web Components in @a2ui/web_core/v0_9/basic_catalog, so the 23 duplicated React implementations are removed along with their unit tests.

What changes for consumers

Import the catalog and the individual components from web_core:

-import {A2uiSurface, basicCatalog} from '@a2ui/react/v0_9';
+import {A2uiSurface} from '@a2ui/react/v0_9';
+import {basicCatalog} from '@a2ui/web_core/v0_9/basic_catalog';

MarkdownContext and useMarkdownRenderer keep their names, their behaviour, and their import path. A2uiSurface forwards the context value into web_core's setMarkdownRenderer, mirroring what the Angular renderer does, so markdown wiring in consumer code does not change.

Custom React components are unaffected: createComponentImplementation still returns a React implementation, and the renderer still renders it through React.

Breaking

• @a2ui/react/v0_9 no longer exports basicCatalog, Text, Button, Card, or the other basic components.
• The basic catalog no longer server-renders, since custom elements produce no markup outside a browser. An application that needs SSR for these components needs a React-SSR renderer.

Testing

• renderers/react unit tests pass; integration-scenarios.test.tsx now drives the web_core catalog end to end and waits for Lit's update cycle.
• The explorer's Karma suite passes against the web component catalog.

[gemini-code-assist]

Code Review

This pull request refactors the React renderer by removing local React implementations of basic catalog components in favor of web_core's basic catalog Custom Elements, updating imports and tests accordingly. To avoid a race condition where Lit components render on their first paint before the markdown renderer is set, it is recommended to use useLayoutEffect instead of useEffect in A2uiSurface to synchronously configure the markdown renderer during React's commit phase.

[gemini-code-assist]

Import useLayoutEffect instead of useEffect to avoid race conditions with Lit's asynchronous rendering cycle.

Suggested change

	import React, {useCallback, useEffect, useMemo, useSyncExternalStore} from 'react';
	import React, {useCallback, useLayoutEffect, useMemo, useSyncExternalStore} from 'react';

[gemini-code-assist]

Using useEffect to set the global markdown renderer can lead to a race condition with Lit's asynchronous update cycle. Lit components schedule their updates as microtasks during their connectedCallback (which runs synchronously when React inserts them into the DOM). Since useEffect runs asynchronously in a macrotask after the paint, Lit's first update cycle will execute before useEffect runs and sets the markdown renderer. This can cause the components to render without the markdown renderer on their first paint.

Using useLayoutEffect ensures that setMarkdownRenderer is called synchronously during React's commit phase, before the microtask queue flushes and before the browser paints, guaranteeing that the markdown renderer is available for Lit's initial render.

Suggested change

	useEffect(() => {
	setMarkdownRenderer(markdownRenderer);
	}, [markdownRenderer]);
	useLayoutEffect(() => {
	setMarkdownRenderer(markdownRenderer);
	}, [markdownRenderer]);