feat: implement Figlet, Pastel, and Unit tools with a unified layout

- Add Figlet text converter with font selection and history
- Add Pastel color palette generator and manipulation suite
- Add comprehensive Units converter with category-based logic
- Introduce AppShell with Sidebar and Header for navigation
- Modernize theme system with CSS variables and new animations
- Update project configuration and dependencies

lib/utils/animations.ts

@@ -0,0 +1,38 @@
+// Animation utility classes and keyframes
+
+export const fadeIn = {
+  initial: { opacity: 0 },
+  animate: { opacity: 1 },
+  exit: { opacity: 0 },
+};
+
+export const slideUp = {
+  initial: { opacity: 0, y: 20 },
+  animate: { opacity: 1, y: 0 },
+  exit: { opacity: 0, y: -20 },
+};
+
+export const slideDown = {
+  initial: { opacity: 0, y: -20 },
+  animate: { opacity: 1, y: 0 },
+  exit: { opacity: 0, y: 20 },
+};
+
+export const scaleIn = {
+  initial: { opacity: 0, scale: 0.95 },
+  animate: { opacity: 1, scale: 1 },
+  exit: { opacity: 0, scale: 0.95 },
+};
+
+export const staggerChildren = {
+  animate: {
+    transition: {
+      staggerChildren: 0.05,
+    },
+  },
+};
+
+export const staggerItem = {
+  initial: { opacity: 0, y: 10 },
+  animate: { opacity: 1, y: 0 },
+};