refactor: streamline toast system and harmonize UI across tools

- Migrate all toast notifications to sonner and remove custom ToastProvider
- Align Card and TextInput styling across Figlet and Pastel (rounded-lg, border-based)
- Fix build error by removing non-existent export in lib/units/index.ts
- Clean up unused Figlet components and constants

lib/storage/history.ts

@@ -1,53 +0,0 @@
-'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));
-}