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/ToolsGrid.tsx

@@ -7,7 +7,7 @@ const tools = [
   {
     title: 'Pastel',
     description: 'Modern color manipulation toolkit with palette generation, accessibility testing, and format conversion. Supports hex, RGB, HSL, Lab, and more.',
-    url: 'https://pastel.kit.pivoine.art',
+    url: '/pastel',
     gradient: 'gradient-indigo-purple',
     accentColor: '#a855f7',
     badges: ['Open Source', 'WCAG', 'Free'],
@@ -24,7 +24,7 @@ const tools = [
   {
     title: 'Units',
     description: 'Smart unit converter with 187 units across 23 categories. Real-time bidirectional conversion with fuzzy search and conversion history.',
-    url: 'https://units.kit.pivoine.art',
+    url: '/units',
     gradient: 'gradient-cyan-purple',
     accentColor: '#2dd4bf',
     badges: ['Open Source', 'Real-time', 'Free'],
@@ -37,7 +37,7 @@ const tools = [
   {
     title: 'Figlet',
     description: 'ASCII art text generator with 373 fonts. Create stunning text banners, terminal art, and retro designs with live preview and multiple export formats.',
-    url: 'https://figlet.kit.pivoine.art',
+    url: '/figlet',
     gradient: 'gradient-yellow-amber',
     accentColor: '#eab308',
     badges: ['Open Source', 'ASCII Art', 'Free'],
@@ -67,8 +67,8 @@ export default function ToolsGrid() {
           <h2 className="text-4xl md:text-5xl font-bold mb-4 bg-clip-text text-transparent bg-gradient-to-r from-purple-400 to-cyan-400">
             Available Tools
           </h2>
-          <p className="text-gray-400 text-lg max-w-2xl mx-auto">
-            Explore our collection of carefully crafted tools designed to boost your productivity and creativity.
+          <p className="text-muted-foreground text-lg max-w-2xl mx-auto">
+            Explore our collection of carefully crafted tools designed to boost your productivity and creativity
           </p>
         </motion.div>