Add CI tests for remote scenarios (SSH/devcontainer/WSL)

[garbas]

Problem:
Extension needs to be tested in remote development scenarios, but there are no CI tests for these use cases.

Expected behavior:
Add automated CI tests for:

• Remote SSH - Extension running on remote machine via SSH
• Dev Container - Extension running inside a devcontainer
• WSL - Extension running in Windows Subsystem for Linux

Implementation considerations:

• May need separate CI jobs for each scenario
• GitHub Actions supports containers (for devcontainer testing)
• WSL testing may require Windows runners
• Remote SSH testing may need to simulate remote connection

Why this matters:

• These are common development scenarios for Flox users
• Extension behavior may differ in remote contexts (especially activation flow)
• Catch remote-specific bugs before users hit them

Current state:

• Integration tests exist for local development
• No automated tests for remote scenarios

Impact:
Without these tests, we risk breaking remote development workflows without knowing it.