Fix Docker gateway IP detection for newer Docker versions

[fao89]

Improve gateway IP detection in get_gateway_ip() to handle both legacy and newer Docker API formats:

• Try legacy NetworkSettings.Gateway first for backwards compatibility
• Fall back to Networks section for newer Docker versions
• Iterate through all networks to find any available gateway
• Maintain "0.0.0.0" fallback for cases where no gateway is found

This resolves issues where newer Docker versions store network information in a different structure than the legacy format.

🤖 Generated with Claude Code

Co-Authored-By: Claude [email protected]