Extract frontend assets to separate repository

[szkiba]

This PR extracts the frontend assets to a separate repository to improve maintainability and development workflow.

Changes

• Refactored to load frontend assets from external package
• Removed all frontend source code from the main repository (UI, report, model, view, config packages)
• Removed Node.js/yarn dependencies and build configuration
• Updated Go module dependencies to include the new external assets package
• Updated tests to work with the new asset loading mechanism

Benefits

• Improved Separation of Concerns: Frontend and backend development can now be managed independently
• Reduced Repository Size: Removed ~18,000 lines of frontend code and dependencies
• Better Build Process: Frontend assets are pre-built and distributed as a Go module
• Simplified Development: Backend developers don't need Node.js tooling to work on Go code

Technical Details

The frontend assets are now loaded from an external repository/package and embedded into the binary at build time. This maintains the same user experience while providing better project structure.

Closes #303