feat(ui): add AI-powered UI Generator app for Makepad

[ParthMozarkar]

This PR introduces an AI-powered UI Generator for Makepad inside MoFA Studio, resolving Issue #12.

The feature allows users to generate Makepad UI layouts using natural language prompts, creating a foundation for AI-assisted UI development directly within the studio environment.

Key Changes

1. New Application Crate

• Added a new crate: apps/mofa-ui-generator
• Implements the standard MofaApp trait for seamless integration with the MoFA modular architecture.
• Structured to allow future expansion of AI-based tools within the ecosystem.

2. AI Chat Interface

• Implemented a dedicated chat panel for describing UI layouts using natural language.
• Added an input system for submitting prompts.
• Designed for future integration with AI model APIs.

3. Code & Preview Workspace

• Introduced a split-view interface:
  • Generated Code Panel to display Makepad DSL output.
  • Preview Panel (planned) reserved for rendering the generated UI in the future.
• Layout prepared for future live preview rendering.

4. Shell Integration
   The UI Generator has been fully integrated into the MoFA Studio shell:

• Added a "UI Generator" tab in the main sidebar
• Registered the app in PageRouter
• Registered the app in AppRegistry
• Integrated into the Dashboard layout

Architecture Notes

• Follows the existing plugin-based architecture used in MoFA Studio.
• Ensures modular scalability for future AI developer tools.

Future Enhancements

• Live UI preview rendering
• AI prompt refinement
• Component-level editing
• Integration with external LLM providers

Feedback on the implementation, architecture, and UI/UX is welcome.

[ParthMozarkar]

could any one check with this?