refactor: upgrade ESLint 9→10 and simplify React lint toolchain

- Upgrade eslint and @eslint/js to v10
- Replace eslint-plugin-react-x + eslint-plugin-react-dom + eslint-plugin-react-hooks
  with unified @eslint-react/eslint-plugin
- Raise dev Node.js requirement to ^22.13.0 || >=24 (runtime packages unaffected)
- Add .npmrc with engine-strict=true
- Move all @eslint-react rule overrides to eslint.config.js,
  eliminating plugin-specific inline eslint-disable comments
- Fix real issues caught by new rules: useless assignments,
  leaked setTimeout, ref naming, useState setter naming

packages/website/src/router.tsx

@@ -18,10 +18,12 @@ function ScrollToTop() {
 
 export default function Router() {
 	useEffect(() => {
-		const schedule = globalThis.requestIdleCallback ?? ((cb: () => void) => setTimeout(cb, 1))
-		const cancel = globalThis.cancelIdleCallback ?? clearTimeout
-		const id = schedule(() => docsImport())
-		return () => cancel(id)
+		if ('requestIdleCallback' in globalThis) {
+			const id = requestIdleCallback(() => docsImport())
+			return () => cancelIdleCallback(id)
+		}
+		const id = setTimeout(() => docsImport(), 1)
+		return () => clearTimeout(id)
 	}, [])
 
 	return (