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/units/storage.ts

@@ -0,0 +1,115 @@
+/**
+ * LocalStorage utilities for persisting user data
+ */
+
+export interface ConversionRecord {
+  id: string;
+  timestamp: number;
+  from: {
+    value: number;
+    unit: string;
+  };
+  to: {
+    value: number;
+    unit: string;
+  };
+  measure: string;
+}
+
+const HISTORY_KEY = 'units-ui-history';
+const FAVORITES_KEY = 'units-ui-favorites';
+const MAX_HISTORY = 50;
+
+/**
+ * Save conversion to history
+ */
+export function saveToHistory(record: Omit<ConversionRecord, 'id' | 'timestamp'>): void {
+  if (typeof window === 'undefined') return;
+
+  const history = getHistory();
+  const newRecord: ConversionRecord = {
+    ...record,
+    id: crypto.randomUUID(),
+    timestamp: Date.now(),
+  };
+
+  // Add to beginning and limit size
+  const updated = [newRecord, ...history].slice(0, MAX_HISTORY);
+  localStorage.setItem(HISTORY_KEY, JSON.stringify(updated));
+}
+
+/**
+ * Get conversion history
+ */
+export function getHistory(): ConversionRecord[] {
+  if (typeof window === 'undefined') return [];
+
+  try {
+    const stored = localStorage.getItem(HISTORY_KEY);
+    return stored ? JSON.parse(stored) : [];
+  } catch {
+    return [];
+  }
+}
+
+/**
+ * Clear conversion history
+ */
+export function clearHistory(): void {
+  if (typeof window === 'undefined') return;
+  localStorage.removeItem(HISTORY_KEY);
+}
+
+/**
+ * Get favorite units
+ */
+export function getFavorites(): string[] {
+  if (typeof window === 'undefined') return [];
+
+  try {
+    const stored = localStorage.getItem(FAVORITES_KEY);
+    return stored ? JSON.parse(stored) : [];
+  } catch {
+    return [];
+  }
+}
+
+/**
+ * Add unit to favorites
+ */
+export function addToFavorites(unit: string): void {
+  if (typeof window === 'undefined') return;
+
+  const favorites = getFavorites();
+  if (!favorites.includes(unit)) {
+    favorites.push(unit);
+    localStorage.setItem(FAVORITES_KEY, JSON.stringify(favorites));
+  }
+}
+
+/**
+ * Remove unit from favorites
+ */
+export function removeFromFavorites(unit: string): void {
+  if (typeof window === 'undefined') return;
+
+  const favorites = getFavorites();
+  const filtered = favorites.filter(u => u !== unit);
+  localStorage.setItem(FAVORITES_KEY, JSON.stringify(filtered));
+}
+
+/**
+ * Toggle favorite status
+ */
+export function toggleFavorite(unit: string): boolean {
+  const favorites = getFavorites();
+  const isFavorite = favorites.includes(unit);
+
+  if (isFavorite) {
+    removeFromFavorites(unit);
+    return false;
+  } else {
+    addToFavorites(unit);
+    return true;
+  }
+}