feat: add shell assistant for natural language command translation

Description

Inspired by similar features from warp shell and AIChat.

• Adds shell assistant scripts and documentation to enable natural language command translation in bash and zsh shells
• The assistant lets users write commands in plain English and translates them to proper shell commands using GitLab Duo
• Includes two shell script versions:
  • assistant.bash for Bash shell users
  • assistant.zsh for Zsh shell users
• Adds comprehensive documentation with installation instructions and usage examples
• Binds to Alt+e for seamless integration into normal terminal workflow

Demo

How has this been tested?

• Tested bash version on Linux, I would like for someone with a Mac to test the zsh version. We should probably also add a powershell version too in a future MR.
• Verified various command categories:
  • File operations
  • System commands
  • Git operations
  • Text processing
  • Network commands
  • File search
  • Process management
  • Permission management

Types of changes

• New feature (non-breaking change which adds functionality)
• Documentation