fix(app-render): prevent double CSS insertion with inlineCss
When `experimental.inlineCss` is enabled, CSS content was being sent
twice on initial page load: once as `<style>` tags in the HTML `<head>`
and again as serialized elements in the RSC inline payload.
This fix introduces a CSS collection mechanism that captures inline CSS
during component tree construction and injects it via ServerInsertedHTML
instead of rendering `<style>` elements in the RSC tree. This ensures
CSS appears only in the HTML output, not in the serialized RSC payload.
Changes:
- Add CollectedInlineCss type to collect CSS data
- Modify renderCssResource to collect CSS instead of rendering when
collectedInlineCss is provided
- Update makeGetServerInsertedHTML to render collected CSS
- Wire collectedInlineCss through the render pipeline
- Add test to verify CSS is not in RSC inline payload
