Add a conditional browser query example - #8617

Summary

https://react-ch7zfadp5-react-foundation.vercel.app/reference/react-dom/browser#conditionally-rendering-in-the-browser

• add a runnable example for conditionally calling use(browser()) from a Suspense-enabled query wrapper
• show how initial data renders immediately while a query without initial data waits for the browser
• keep the query implementation and server-rendering harness hidden so the visible example stays focused

Validation

• npx prettier --config .prettierrc --check src/content/reference/react-dom/browser.md
• npx eslint src/content/reference/react-dom/browser.md
• yarn lint-heading-ids
• verified locally that Reload first shows React mug with the loading fallback, then resolves React shirt