fix(iso): add stress-ng to package list for CPU SAT

stress-ng was missing from the LiveCD — CPU acceptance test exited
immediately with rc=1 because the binary was not found.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/builder/config/package-lists/bee.list.chroot

@@ -36,6 +36,7 @@ sudo
 zstd
 mstflint
 memtester
+stress-ng
 
 # QR codes (for displaying audit results)
 qrencode