fix(ui): bundle marked by switching from async to sync API

marked({ async: true }) triggers a dynamic internal require inside marked
that vite/rollup treats as external, causing ERR_MODULE_NOT_FOUND at runtime
in the adapter-node Docker image which ships no node_modules.
Switching to the synchronous marked() call makes rollup inline the full
library into the server chunk.

ui/src/routes/api/chapter/[slug]/[n]/+server.ts

@@ -104,7 +104,7 @@ export const GET: RequestHandler = async ({ params, url, locals }) => {
 		const res = await fetch(presignUrl);
 		if (!res.ok) throw new Error(`MinIO returned ${res.status}`);
 		const markdown = await res.text();
-		html = await marked(markdown, { async: true });
+		html = marked(markdown) as string;
 	} catch (e) {
 		log.error('api/chapter', 'failed to fetch chapter content', { slug, n, err: String(e) });
 	}

ui/src/routes/books/[slug]/chapters/[n]/+page.server.ts

@@ -114,7 +114,7 @@ export const load: PageServerLoad = async ({ params, url, locals }) => {
 		const res = await fetch(presignUrl);
 		if (!res.ok) throw new Error(`MinIO returned ${res.status}`);
 		const markdown = await res.text();
-		html = await marked(markdown, { async: true });
+		html = marked(markdown) as string;
 	} catch (e) {
 		// Don't hard-fail — show empty content with error message
 		log.error('chapter', 'failed to fetch chapter content', { slug, n, err: String(e) });