test: Add tests for web-components/define.ts registration

[annondeveloper]

The defineCustomElements() function in src/web-components/define.ts registers 20 React components as web custom elements, but has no test coverage.

What to test:

• defineCustomElements() registers all 20 elements without throwing
• Custom prefix parameter works (defineCustomElements('my') → <my-button>)
• Duplicate registration is handled gracefully
• Each registered element has the correct observedAttributes

Reference: See src/__tests__/web-components/wrapper.test.ts for test style.
File to create: src/__tests__/web-components/define.test.ts

Skills needed: TypeScript, vitest, Web Components API