🤖 refactor: Convert ProjectSidebar to Tailwind CSS

- Replaced 23 styled components with Tailwind utility classes
- Converted conditional props (selected, isDragging, isOver) to cn() helper
- Used inline styles for dynamic transform values on rotation
- Preserved all drag-and-drop functionality and hover states
- Maintained accessibility attributes and data attributes for tests
- Reduced file from 989 to 666 lines (32% reduction, -323 lines)

Author: kylecarbs