native-mpa-preview.md

@lynx-js/go-web	minor

Add opt-in preview extension points for native modules and multi-page (MPA) examples.

• Level A — GoConfig.previewNativeEnv and the per-instance nativeEnv prop forward a generic native environment (onNativeModulesCall, nativeModulesMap, napiModulesMap, onNapiModulesCall, and a static-or-factory globalProps / initData) to the previewed <lynx-view> before it starts.
• Level B — GoConfig.PreviewRuntime replaces the built-in single-card renderer with a custom component (receiving every previewable entry plus the resolved native environment) so embedders can stack cards and route cross-page navigation, while go-web keeps owning the tab bar, QR, code browser, scaling, and SSG path.

Both are backwards compatible and product-agnostic: when unset, the preview is identical to before, and go-web hard-codes no framework module names or URL scheme.