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/lib/animations.ts

@@ -0,0 +1,62 @@
+import { Variants, Transition } from 'framer-motion';
+
+// Page transition animations
+export const pageVariants: Variants = {
+  initial: { opacity: 0, y: 10 },
+  animate: { opacity: 1, y: 0 },
+  exit: { opacity: 0, y: -10 },
+};
+
+// List item stagger animations
+export const listItemVariants: Variants = {
+  hidden: { opacity: 0, x: -10 },
+  visible: { opacity: 1, x: 0 },
+};
+
+// Container stagger animations
+export const containerVariants: Variants = {
+  hidden: { opacity: 0 },
+  visible: {
+    opacity: 1,
+    transition: {
+      staggerChildren: 0.05,
+    },
+  },
+  exit: {
+    opacity: 0,
+    transition: {
+      duration: 0.1,
+    },
+  },
+};
+
+// Fade in animations
+export const fadeInVariants: Variants = {
+  initial: { opacity: 0 },
+  animate: { opacity: 1 },
+  exit: { opacity: 0 },
+};
+
+// Button tap animation
+export const buttonTap = { scale: 0.98 };
+
+// Card hover animation
+export const cardHover = { y: -2, boxShadow: '0 10px 25px -5px rgb(0 0 0 / 0.1)' };
+
+// Default transition config
+export const defaultTransition: Transition = {
+  duration: 0.2,
+  ease: [0.4, 0, 0.2, 1],
+};
+
+// Fast transition
+export const fastTransition: Transition = {
+  duration: 0.15,
+  ease: [0.4, 0, 0.2, 1],
+};
+
+// Slow transition
+export const slowTransition: Transition = {
+  duration: 0.3,
+  ease: [0.4, 0, 0.2, 1],
+};

desktop/src/lib/utils.ts

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+import { clsx, type ClassValue } from 'clsx';
+import { twMerge } from 'tailwind-merge';
+
+export function cn(...inputs: ClassValue[]) {
+  return twMerge(clsx(inputs));
+}