feat(ui): enhance UI with animations, dark mode support and and improved components

- Add framer-motion page transitions and AnimatePresence support
- Add dark mode support across all components
- Create reusable UI components (Button, Badge, Card, EmptyState, Input, Toast, Skeleton)
- Add CSS custom properties for consistent theming
- Add animation variants and utility functions
- Improve ChatArea, Sidebar, TriggersPanel with animations

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

desktop/src/index.css

@@ -1,4 +1,64 @@
-@import "tailwindcss";
+@import "tailwindcss";
+
+:root {
+  /* Brand Colors */
+  --color-primary: #f97316;
+  --color-primary-hover: #ea580c;
+  --color-primary-light: #fff7ed;
+
+  /* Semantic Colors */
+  --color-success: #22c55e;
+  --color-warning: #eab308;
+  --color-error: #ef4444;
+  --color-info: #3b82f6;
+
+  /* Neutral Colors */
+  --color-bg: #ffffff;
+  --color-bg-secondary: #f9fafb;
+  --color-border: #e5e7eb;
+  --color-text: #111827;
+  --color-text-secondary: #6b7280;
+  --color-text-muted: #9ca3af;
+
+  /* Spacing Scale */
+  --space-xs: 4px;
+  --space-sm: 8px;
+  --space-md: 16px;
+  --space-lg: 24px;
+  --space-xl: 32px;
+
+  /* Border Radius */
+  --radius-sm: 6px;
+  --radius-md: 8px;
+  --radius-lg: 12px;
+  --radius-xl: 16px;
+  --radius-full: 9999px;
+
+  /* Shadows */
+  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
+  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1);
+  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1);
+
+  /* Transitions */
+  --transition-fast: 150ms ease;
+  --transition-normal: 200ms ease;
+  --transition-slow: 300ms ease;
+}
+
+.dark {
+  --color-bg: #0f172a;
+  --color-bg-secondary: #1e293b;
+  --color-border: #334155;
+  --color-text: #f1f5f9;
+  --color-text-secondary: #94a3b8;
+  --color-text-muted: #64748b;
+}
+
+/* Focus states for accessibility */
+:focus-visible {
+  outline: 2px solid var(--color-primary);
+  outline-offset: 2px;
+}
 
 body {
   font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;