- Only set HTTPS_PROXY/HTTP_PROXY when iptables UID isolation is NOT
available. With iptables, double-proxying caused profile picture
fetches to fail with 'lookup http' DNS errors.
- Fix is_agent detection: handle JSON with spaces after colons
("requestType": "agent" vs "requestType":"agent")
- Suppress wrapper-not-installed warning in standalone mode
- Show 'iptables (standalone)' in banner instead of 'not installed'