fix: two bugs in Cloud Storage PDF viewing surfaced by live testing

- PDF viewer hung on "Loading" forever for cloud-backed PDFs: streamFileTo
  pipes with {end: false} (by design, so cloud-storage.ts's own routes can
  call res.end() themselves), but the new /pdf-files/:id cloud branch never
  did, so the HTTP response never completed.
- Documents page showed nothing for patients whose PDFs are only in Cloud
  Storage: the page lists categories from the legacy PdfGroup table, which
  new saves stopped populating. savePdfToCloudStorage now also ensures a
  blob-less PdfGroup row exists per patient/category so the category still
  appears, with actual files served from Cloud Storage via the existing
  merge in the pdf-files/group listing routes.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/Backend/src/routes/documents.ts

@@ -290,9 +290,11 @@ router.get(
         );
         try {
           await storage.streamFileTo(res, cloudId);
+          if (!res.writableEnded) res.end();
         } catch (streamErr) {
           console.error("Error streaming cloud PDF file:", streamErr);
           if (!res.headersSent) res.status(500).json({ error: "Failed to stream PDF" });
+          else if (!res.writableEnded) res.end();
         }
         return;
       }