Initial scaffold: Researcher Endorsement frontend

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/components/PDFPreview.tsx

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+import React, { useEffect } from 'react'
+
+const PDFPreview: React.FC<{ url: string; name?: string }> = ({ url, name }) => {
+  useEffect(() => {
+    return () => {
+      // only revoke blob URLs
+      try {
+        if (url && url.startsWith('blob:')) URL.revokeObjectURL(url)
+      } catch (e) {
+        // ignore
+      }
+    }
+  }, [url])
+
+  return (
+    <div>
+      <div className="small">{name}</div>
+      <iframe src={url} width="100%" height={300} title={name ?? 'pdf'} />
+    </div>
+  )
+}
+
+export default PDFPreview