Add comprehensive component library expansion with new UI components

This commit includes multiple new components and improvements to the UI essentials library:

## New Components Added:
- **Accordion**: Expandable/collapsible content panels with full accessibility
- **Alert**: Notification and messaging component with variants and dismiss functionality
- **Popover**: Floating content containers with positioning and trigger options
- **Timeline**: Chronological event display with customizable styling
- **Tree View**: Hierarchical data display with expand/collapse functionality
- **Toast**: Notification component (previously committed, includes style refinements)

## Component Features:
- Full TypeScript implementation with Angular 19+ patterns
- Comprehensive SCSS styling using semantic design tokens exclusively
- Multiple size variants (sm, md, lg) and color variants (primary, success, warning, danger, info)
- Accessibility support with ARIA attributes and keyboard navigation
- Responsive design with mobile-first approach
- Interactive demos showcasing all component features
- Integration with existing design system and routing

## Demo Applications:
- Created comprehensive demo components for each new component
- Interactive examples with live code demonstrations
- Integrated into main demo application routing and navigation

## Documentation:
- Added COMPONENT_CREATION_TEMPLATE.md with detailed guidelines
- Comprehensive component creation patterns and best practices
- Design token usage guidelines and validation rules

## Code Quality:
- Follows established Angular and SCSS conventions
- Uses only verified semantic design tokens
- Maintains consistency with existing component architecture
- Comprehensive error handling and edge case management

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

projects/demo-ui-essentials/src/app/demos/toast-demo/toast-demo.component.scss

@@ -1,4 +1,4 @@
-@use '../../../../../../../../shared-ui/src/styles/semantic' as *;
+@use '../../../../../shared-ui/src/styles/semantic/index' as *;
 
 .demo-container {
   padding: $semantic-spacing-layout-section-md;