fix: resolve docker context when running as root via launchd

[gregnr]

When installed via Homebrew, the binary runs as a root LaunchDaemon which has no ~/.docker/config.json. This meant docker context resolution always failed, and there was no fallback. So even if you were using the default docker socket, it wouldn't use it.

This fixes the issue by:

1. Detecting the logged in user via who owns /dev/console, then points DOCKER_CONFIG to their docker config directory before resolving the context
2. If context resolution still fails, it falls back to client.FromEnv which respects DOCKER_HOST and then the default socket

Test plan

• sudo ./docker-mac-net-connect works (normal sudo, HOME preserved)
• sudo -i $(pwd)/docker-mac-net-connect works (simulates launchd with root HOME)
• Falls back gracefully if no console user or no docker config exists