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/list/[id]/page.tsx

@@ -15,32 +15,32 @@ export default async function ListDetailPage({ params }: { params: { id: string
   const completedItems = list.items.filter(item => item.completed)
 
   return (
-    <main className="container mx-auto px-4 py-8 max-w-4xl">
+    <main className="container mx-auto px-4 sm:px-6 py-6 sm:py-8 max-w-6xl">
       {/* Header */}
-      <div className="mb-8">
+      <div className="mb-6 sm:mb-8">
         <Link 
           href="/" 
-          className="inline-flex items-center gap-2 text-gray-600 hover:text-gray-900 mb-4 transition-colors"
+          className="inline-flex items-center gap-2 text-gray-600 hover:text-gray-900 active:text-black mb-4 transition-colors tap-target-sm text-sm sm:text-base"
         >
-          <ArrowLeft size={20} />
+          <ArrowLeft size={20} className="flex-shrink-0" />
           <span>Back to Lists</span>
         </Link>
         
-        <div className="flex items-center gap-3 mb-2">
+        <div className="flex items-center gap-2 sm:gap-3 mb-2">
           <div 
-            className="w-6 h-6 rounded-full flex-shrink-0" 
+            className="w-5 h-5 sm:w-6 sm:h-6 rounded-full flex-shrink-0" 
             style={{ backgroundColor: list.color }}
           />
-          <h1 className="text-3xl font-bold text-gray-900">{list.title}</h1>
+          <h1 className="text-2xl sm:text-3xl lg:text-4xl font-bold text-gray-900 truncate">{list.title}</h1>
         </div>
         
-        <p className="text-gray-600">
+        <p className="text-gray-600 text-sm sm:text-base">
           {completedItems.length} of {list.items.length} tasks completed
         </p>
       </div>
 
       {/* Inline Item Creation */}
-      <div className="mb-6">
+      <div className="mb-6 sm:mb-8">
         <InlineItemCreate listId={list.id} />
       </div>