refactor(ui): improve UI/UX design and spacing

- Increase card padding and gaps for better visual hierarchy
- Add hover lift effect to cards with smooth transitions
- Improve typography with larger headings and better line-height
- Darken meta text colors for better readability
- Add checkbox styling with accent color
- Make tags interactive with hover effects
- Add mobile responsive styles for forms and footer
- Replace Unicode arrows with SVG icons
- Improve focus styles for accessibility
- Increase badge padding and font-weight
- Add subtle shadow to cards by default

app/presentation/templates/pages/post_detail.html

@@ -39,7 +39,10 @@
         
         <div class="flex justify-between items-center" data-testid="post-detail-actions">
             <a href="/" class="btn" data-testid="btn-back-to-posts">
-                ← Back to posts
+                <svg width="16" height="16" viewBox="0 0 16 16" fill="none" xmlns="http://www.w3.org/2000/svg" style="margin-right: 0.5rem;">
+                    <path d="M10 12L6 8L10 4" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"/>
+                </svg>
+                Back to posts
             </a>
             
             <div class="flex gap-2" data-testid="post-detail-edit-actions">