fix: preserve custom env vars in multi-user mode via sudo -E

[Blumlaut]

Problem

In multi-user mode (OPEN_TERMINAL_MULTI_USER=true), custom environment variables passed via the env field in POST /execute are silently dropped.

PtyRunner wraps commands with sudo -u <user> -- bash -c "...", but sudo resets the environment by default for security. The env dict is passed to subprocess.Popen, but never reaches the actual subprocess.

This breaks any workflow that relies on injecting env vars (e.g. GH_TOKEN for GitHub CLI authentication, API keys, custom config).

Solution

Add -E flag to sudo to preserve the environment through the user switch.