Refactor SwipeTabs for smoother touch transitions

- Rewrite SwipeTabs with improved touch handling and animation
- Use translate3d with smoother easing curve (280ms)
- Add coalesced pointer events for high refresh rate displays
- Clean up redundant CSS styles across multiple files
- Add page-max-width dimension variable

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/pages/admin/Features.tsx

@@ -119,7 +119,7 @@ export default function Features() {
         const userEnabled = state?.user ?? true;
 
         return (
-            <div className="theme-tab-content">
+            <div className="theme-tab-content content-narrow">
                 <div className="theme-section">
                     <div className="section-header">
                         <h3 className="section-title">{t.featuresPage?.visibility || 'Visibilità'}</h3>

frontend/src/pages/admin/Settings.tsx

@@ -70,7 +70,7 @@ export default function Settings() {
                     </div>
                 </div>
 
-                <div className="page-content">
+                <div className="page-content page-content--narrow">
                     <div className="settings-card">
                         <div className="settings-section">
                             <h2>{t.settings.authentication}</h2>