chore(page-templates): tidy ts suppression in duplicatePage pageEmbed remap (#37)

Replace bare //@ts-ignore (no space, no reason) with // @ts-expect-error plus a
reason on the pageEmbed sourcePageId reassignment, matching the codebase style.
ProseMirror Attrs is read-only typed, so the reassignment genuinely errors —
@ts-expect-error is valid here.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/server/src/core/page/services/page.service.ts

@@ -716,7 +716,7 @@ export class PageService {
             const sourcePageId = node.attrs.sourcePageId;
             if (sourcePageId && pageMap.has(sourcePageId)) {
               const mappedPage = pageMap.get(sourcePageId);
-              //@ts-ignore
+              // @ts-expect-error ProseMirror Attrs is read-only typed; reassigning sourcePageId to the duplicated page copy is intentional here
               node.attrs.sourcePageId = mappedPage.newPageId;
             }
           }