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

components/ui/Toast.tsx

@@ -0,0 +1,90 @@
+'use client';
+
+import * as React from 'react';
+import { X, CheckCircle2, AlertCircle, Info } from 'lucide-react';
+import { cn } from '@/lib/utils/cn';
+
+export type ToastType = 'success' | 'error' | 'info';
+
+export interface Toast {
+  id: string;
+  message: string;
+  type: ToastType;
+}
+
+interface ToastContextType {
+  toasts: Toast[];
+  addToast: (message: string, type?: ToastType) => void;
+  removeToast: (id: string) => void;
+}
+
+const ToastContext = React.createContext<ToastContextType | undefined>(undefined);
+
+export function ToastProvider({ children }: { children: React.ReactNode }) {
+  const [toasts, setToasts] = React.useState<Toast[]>([]);
+
+  const addToast = React.useCallback((message: string, type: ToastType = 'success') => {
+    const id = Math.random().toString(36).substring(7);
+    setToasts((prev) => [...prev, { id, message, type }]);
+
+    // Auto remove after 3 seconds
+    setTimeout(() => {
+      setToasts((prev) => prev.filter((t) => t.id !== id));
+    }, 3000);
+  }, []);
+
+  const removeToast = React.useCallback((id: string) => {
+    setToasts((prev) => prev.filter((t) => t.id !== id));
+  }, []);
+
+  return (
+    <ToastContext.Provider value={{ toasts, addToast, removeToast }}>
+      {children}
+      <div className="fixed bottom-4 right-4 z-50 flex flex-col gap-2 pointer-events-none">
+        {toasts.map((toast) => (
+          <ToastItem key={toast.id} toast={toast} onClose={() => removeToast(toast.id)} />
+        ))}
+      </div>
+    </ToastContext.Provider>
+  );
+}
+
+function ToastItem({ toast, onClose }: { toast: Toast; onClose: () => void }) {
+  const Icon = toast.type === 'success' ? CheckCircle2 : toast.type === 'error' ? AlertCircle : Info;
+
+  return (
+    <div
+      className={cn(
+        'flex items-center gap-3 px-4 py-3 rounded-lg shadow-lg pointer-events-auto',
+        'animate-in slide-in-from-right-full duration-300',
+        'min-w-[300px] max-w-[400px]',
+        {
+          'bg-green-50 text-green-900 border border-green-200 dark:bg-green-900/20 dark:text-green-100 dark:border-green-800':
+            toast.type === 'success',
+          'bg-red-50 text-red-900 border border-red-200 dark:bg-red-900/20 dark:text-red-100 dark:border-red-800':
+            toast.type === 'error',
+          'bg-blue-50 text-blue-900 border border-blue-200 dark:bg-blue-900/20 dark:text-blue-100 dark:border-blue-800':
+            toast.type === 'info',
+        }
+      )}
+    >
+      <Icon className="h-5 w-5 flex-shrink-0" />
+      <p className="text-sm font-medium flex-1">{toast.message}</p>
+      <button
+        onClick={onClose}
+        className="flex-shrink-0 opacity-70 hover:opacity-100 transition-opacity"
+        aria-label="Close"
+      >
+        <X className="h-4 w-4" />
+      </button>
+    </div>
+  );
+}
+
+export function useToast() {
+  const context = React.useContext(ToastContext);
+  if (!context) {
+    throw new Error('useToast must be used within ToastProvider');
+  }
+  return context;
+}