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/index.ts

@@ -0,0 +1,4 @@
+export * from './units';
+export * from './storage';
+export * from './utils';
+export * from './tempo';