Enhance theme handling and SVG styling in dependency graph visualization

- Added dynamic background color adjustments for both dark and light themes in the webview.
- Implemented theme-specific styles for SVG elements, including nodes and edges, to improve visibility and user experience.
- Updated the logic to ensure styles are applied correctly when the theme changes, enhancing the overall responsiveness of the graph rendering.
- Improved comments for clarity and consistency throughout the code.

Author: mununki