Function render_page_to_html 

pub async fn render_page_to_html(
    state: &AppState,
    url_path: &str,
) -> Result<Option<String>>

Render a page to static HTML for pre-rendering / build output.

Resolves URL path to a page file, loads application config, builds a minimal context (no session, no user, no query params), and renders through the engine. Returns None if the page requires authentication or is excluded.