feat: Add Caipe Agent Forge plugin

[sriaradhyula]

This PR adds the Caipe Agent Forge plugin to the Backstage application.

Changes

• Added @caipe/plugin-agent-forge dependency (version 0.3.3)
• Integrated ChatAssistantPage component as a fixed overlay
• Added authentication wrapper to ensure the chat assistant only shows for authenticated users
• Added global styles override for proper text color rendering

Features

• AI-powered chat assistant accessible from any page
• Authentication-aware rendering
• Fixed positioning in bottom-right corner
• Proper styling integration with existing themes

The plugin provides an AI chat interface that can assist users with various tasks within the Backstage environment.