- Add `flatten_shadow_dom` option to CrawlerRunConfig that serializes
shadow DOM content into the light DOM before HTML capture. Uses a
recursive serializer that resolves <slot> projections and strips
only shadow-scoped <style> tags. Also injects an init script to
force-open closed shadow roots via attachShadow patching.
- Move `js_code` execution to after `wait_for` + `delay_before_return_html`
so user scripts run on the fully-hydrated page. Add `js_code_before_wait`
for the less common case of triggering loading before waiting.
- Add JS snippet (flatten_shadow_dom.js), integration test, example,
and documentation across all relevant doc files.