feat: GAIA Code CLI fix

[itomek]

Quick Check ✨

• I've taken a look at existing feature requests
• This feature request relates to GAIA UI (Open-WebUI)

What's on your mind?

GAIA code CLI should follow the new pattern of using its own command, gaia-code, rather than using the general GAIA command with the parameter code.

The following needs to be updated:

• 1. Tests
• 2. Code
• 3. Documentation