feat: add help command mode with dedicated help agent

[tusharmath]

Overview

This PR implements a dedicated help command mode for the Forge CLI application that allows users to get assistance and documentation directly from the CLI.

Features

• Added a new '/help' command to switch to help mode
• Created a help agent with a specialized system prompt template
• Integrated README content into templates to provide documentation context
• Added event handling for user help queries
• Updated the agent model to use google/gemini-2.0-flash-thinking-exp for better response quality
• Enhanced the UI to display mode-specific messages

Implementation Details

• Added new SystemContext.readme field to include README content in prompts
• Created a system-prompt-help.hbs template with specific instructions for help responses
• Updated the state handling to include the new HELP mode
• Configured the help_agent in forge.yaml with appropriate tools and subscriptions
• Enhanced UI messaging to indicate current mode with descriptive text

Testing

The help mode has been tested by:

• Switching to help mode using the /help command
• Asking various questions about Forge CLI functionality
• Verifying that responses include content from the README
• Confirming proper mode switching behavior

Screenshots

(Add screenshots if available)

Related Issues

Closes #[issue_number]