Add comprehensive semantic design token system

Implement complete semantic layer for all design tokens including typography, spacing, motion, colors, borders, shadows, z-index, opacity, and glass effects. Each semantic token maps base design tokens to contextual usage patterns for improved maintainability and developer experience.

Features:
- Complete semantic typography system with font weights, sizes, line heights, and letter spacing
- Comprehensive spacing tokens for components, layouts, and interactions
- Full motion system with durations, easing, transitions, and hover transforms
- Semantic color system with individual access to all Material Design 3 colors
- Border tokens with widths, radius, and styles for all use cases
- Shadow system including standard and AI-themed shadows
- Z-index layering system for proper stacking context
- Opacity tokens for transparency and visibility states
- Glass morphism tokens with blur, opacity, and theming support

All semantic tokens provide direct access to base token values while offering meaningful contextual aliases for common UI patterns.

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

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

projects/shared-ui/src/styles/semantic/shadows/_index.scss

@@ -0,0 +1,14 @@
+// ==========================================================================
+// SEMANTIC SHADOWS INDEX
+// ==========================================================================
+// Contextual shadow system for elevation and depth hierarchy
+// ==========================================================================
+
+// Note: base tokens imported at semantic/index level
+
+// Import semantic colors for context-aware shadows
+//@import '../colors/semantic-colors';
+
+// Semantic shadow mappings
+@import 'semantic-shadows';
+