fix: streaming upload (-T) + non-fatal ISO to prevent OOM on oven
curl --data-binary loads entire file into RAM, OOM on 1GB+ ISO.
Switch to -T (streaming upload). Make ISO upload non-fatal so slim
kernel + initramfs always get uploaded even if ISO fails.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>