feat(UI): Display a side-by-side "diff" view for translations #43

Is your feature request related to a problem?

When code is translated, especially between syntactically similar languages (like Java and C#), it can be difficult for the user to quickly see what has changed. The current UI only shows the final block of translated code.

Describe the solution you'd like

1. Integrate a code diffing library, such as diff2html.js or the Monaco Editor's built-in diffing tool.

2. Add a "Compare" or "Diff" toggle button to the translation UI.

3. When toggled on, the view should change to a two-panel, side-by-side display. The original code should be on the left and the translated code on the right, with additions and deletions clearly highlighted, similar to a GitHub diff.

Additional context

This would be a powerful "pro" feature that elevates the extension from a simple translator to a sophisticated code analysis and learning tool.