ci(react): add browser-based integration testing to a2ui_explorer

[ditman]

Description

This PR adds a karma + jasmine + headless chrome integration test harness to the React a2ui_explorer test app, similar to what we did with Lit here:

• ci(lit): add browser-based integration testing to lit explorer #1545

Key changes

• Made the a2ui_explorer react app a stand-alone package, so we can customize its dependencies (and tests) separately from the react renderer itself
  • Also added some tweaks to the app so it can be inspected by the tests
• Added karma+jasmine+headless chrome to run integration tests
• Added a sample unit test to verify the setup works

Pre-launch Checklist

• I signed the CLA.
• I read the Contributors Guide.
• I read the Style Guide.
• I have added updates to the CHANGELOG.
• I updated/added relevant documentation.
• My code changes (if any) have tests.
• If my branch is on fork, I have verified that scripts/e2e_test.sh passes.

If you need help, consider asking for advice on the discussion board.

[ditman]

I forgot to split the testing for react in unit vs integration in the github workflow!

[gemini-code-assist]

Code Review

This pull request refactors the React explorer application to statically generate and map specification examples instead of using Vite's dynamic import.meta.glob, enabling integration testing with Karma and Jasmine. It introduces a static generation script, configures Karma, adds a robust integration test suite, and refactors the main application component to support testing properties. The reviewer feedback highlights two key improvements: adding tsconfig.spec.json to the test:base wireit task files to ensure proper cache invalidation, and safely validating the initialExampleId in App.tsx to avoid potential runtime crashes from non-null assertions.

[ditman]

(This commit was a little bit weird: 52d4975)

[ditman]

Here's the "integration" test run for react:

• https://github.com/a2ui-project/a2ui/actions/runs/27319214371/job/80706442650?pr=1607#step:6:23

[ditman]

/gemini review again

[gemini-code-assist]

Code Review

This pull request refactors the React Explorer to support integration testing with Karma and esbuild by replacing Vite-specific dynamic imports with a statically generated examples mapping. It also introduces new integration tests and test utilities. Feedback on the changes highlights a potential runtime crash in App.tsx if an invalid initialExampleId is provided, as the non-null assertion could lead to a TypeError when accessing selectedItem.messages. A fallback to the first demo item is suggested to prevent this issue.

[gemini-code-assist]

If initialExampleId is invalid or not found in demoItems, demoItems.find will return undefined. The non-null assertion ! will bypass TypeScript compilation checks, but at runtime, accessing selectedItem.messages will throw a TypeError: Cannot read properties of undefined (reading 'messages') and crash the application.

To prevent this, we should safely fall back to the first demo item (demoItems[0]) if the specified ID is not found, and use optional chaining for the initial state.

Suggested change

	const [selectedExampleId, setSelectedExampleId] = useState(initialExampleId ?? demoItems[0].id);
	const selectedItem = demoItems.find(e => e.id === selectedExampleId)!;
	const [selectedExampleId, setSelectedExampleId] = useState(initialExampleId ?? demoItems[0]?.id);
	const selectedItem = demoItems.find(e => e.id === selectedExampleId) ?? demoItems[0];