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/storage/history.ts

@@ -0,0 +1,53 @@
+'use client';
+
+export interface HistoryItem {
+  id: string;
+  text: string;
+  font: string;
+  result: string;
+  timestamp: number;
+}
+
+const HISTORY_KEY = 'figlet-ui-history';
+const MAX_HISTORY = 10;
+
+export function getHistory(): HistoryItem[] {
+  if (typeof window === 'undefined') return [];
+
+  try {
+    const stored = localStorage.getItem(HISTORY_KEY);
+    return stored ? JSON.parse(stored) : [];
+  } catch {
+    return [];
+  }
+}
+
+export function addToHistory(text: string, font: string, result: string): void {
+  let history = getHistory();
+
+  const newItem: HistoryItem = {
+    id: `${Date.now()}-${Math.random()}`,
+    text,
+    font,
+    result,
+    timestamp: Date.now(),
+  };
+
+  // Add to beginning
+  history.unshift(newItem);
+
+  // Keep only MAX_HISTORY items
+  history = history.slice(0, MAX_HISTORY);
+
+  localStorage.setItem(HISTORY_KEY, JSON.stringify(history));
+}
+
+export function clearHistory(): void {
+  localStorage.removeItem(HISTORY_KEY);
+}
+
+export function removeHistoryItem(id: string): void {
+  const history = getHistory();
+  const filtered = history.filter(item => item.id !== id);
+  localStorage.setItem(HISTORY_KEY, JSON.stringify(filtered));
+}