Count "Download from my account" as a backup for the Home nudge

Only "Download backup" recorded the date, so downloading from the account left
Home saying "You haven't downloaded a backup yet". Both now record it.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/components/settings/DataSection.jsx

@@ -81,7 +81,7 @@ export default function DataSection() {
       <div className="flex flex-wrap items-center gap-3">
         <button type="button" onClick={download} className={btn}>Download backup</button>
         {authUser && (
-          <a href="/api/account/export" download className={`${btn} inline-block`} title="Everything saved to your account on the server, including studies from other devices">Download from my account</a>
+          <a href="/api/account/export" download onClick={() => markBackedUp()} className={`${btn} inline-block`} title="Everything saved to your account on the server, including studies from other devices">Download from my account</a>
         )}
         <button type="button" onClick={() => fileRef.current?.click()} className={btn}>Restore from a backup…</button>
         <input ref={fileRef} type="file" accept="application/json,.json" onChange={choose} className="hidden" aria-label="Backup file" />