feat: implement responsive design enhancements

- Add touch-optimized tap targets (44x44px minimum for iOS)
- Enhance mobile responsiveness across all components
- Improve button sizing and spacing for touch interactions
- Add responsive text sizing and layout adjustments
- Implement mobile-first modal behavior (bottom sheet on mobile)
- Enhance form controls with better touch targets
- Add active states for better touch feedback
- Improve grid layouts for various screen sizes
- Add smooth scrolling and better focus states
- Optimize FilterPanel for mobile with grid layouts
- Enhance all interactive elements with tap-target classes

Requirements: 7.1, 7.2

app/page.tsx

@@ -7,27 +7,27 @@ export default async function Home() {
   const lists = await getLists()
 
   return (
-    <main className="container mx-auto px-4 py-8 max-w-4xl">
-      <div className="flex items-center justify-between mb-8">
-        <h1 className="text-3xl font-bold text-gray-900">Ultimate Lists</h1>
+    <main className="container mx-auto px-4 sm:px-6 py-6 sm:py-8 max-w-7xl">
+      <div className="flex flex-col sm:flex-row items-start sm:items-center justify-between gap-4 mb-6 sm:mb-8">
+        <h1 className="text-2xl sm:text-3xl lg:text-4xl font-bold text-gray-900">Ultimate Lists</h1>
         <NewListButton />
       </div>
 
       {/* Global Search */}
-      <div className="mb-8">
+      <div className="mb-6 sm:mb-8">
         <GlobalSearch />
       </div>
 
-      <div className="grid grid-cols-1 md:grid-cols-2 lg:grid-cols-3 gap-6">
+      <div className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-3 xl:grid-cols-4 gap-4 sm:gap-6">
         {lists.map((list) => (
           <ListCard key={list.id} list={list} />
         ))}
       </div>
 
       {lists.length === 0 && (
-        <div className="text-center py-12">
-          <p className="text-gray-500 text-lg mb-4">No lists yet</p>
-          <p className="text-gray-400">Create your first list to get started</p>
+        <div className="text-center py-12 sm:py-16">
+          <p className="text-gray-500 text-base sm:text-lg mb-3 sm:mb-4">No lists yet</p>
+          <p className="text-gray-400 text-sm sm:text-base">Create your first list to get started</p>
         </div>
       )}
     </main>