Upload file to R2

/* 1. Get bytes */
      const pdfBytes = await pdfRes.arrayBuffer();

      /* 2. Persist to R2 */
      const key = `${userId}/${clientId}-${Date.now()}.pdf`;
      const putRes = await env.REPORTS.put(key, pdfBytes, {
        httpMetadata: { contentType: 'application/pdf' }
      });                               // put() default is private. ✔
      console.log('stored to R2 key →', key, 'etag →', putRes?.etag);

      /* 3. Return a link the front-end can hit */
      return Response.json({ ok: true, url: `/reports/${key}` });