🎨 refactor: migrate sidebar inline styles to CSS classes and improve code organization

This commit improves the codebase structure by:
- Moving all inline styles from SiderBar.js to CSS classes in index.css
- Organizing CSS with clear section comments for better maintainability
- Removing unused imports and components
- Improving sidebar design with cleaner styling and consistent color management
- Restructuring CSS to group related styles together
- Adjusting sidebar width from 200px to 180px
- Replacing Text components with semantic divs for group labels
- Creating a color management function for sidebar icons

web/src/components/layout/PageLayout.js

@@ -124,7 +124,7 @@ const PageLayout = () => {
               : styleState.showSider
                 ? styleState.siderCollapsed
                   ? '60px'
-                  : '200px'
+                  : '180px'
                 : '0',
             transition: 'margin-left 0.3s ease',
             flex: '1 1 auto',