Add playlist export and SEO meta tags

Add text/CSV export endpoints for playlists and saved recommendations.
Add export buttons to PlaylistDetail and Recommendations pages.
Add Open Graph and Twitter meta tags to index.html for better SEO.

frontend/src/pages/Recommendations.tsx

@@ -1,7 +1,7 @@
 import { useState, useEffect } from 'react'
-import { Loader2, Clock, Heart, Sparkles } from 'lucide-react'
+import { Loader2, Clock, Heart, Sparkles, Download } from 'lucide-react'
 import { useAuth } from '../lib/auth'
-import { getRecommendationHistory, getSavedRecommendations, toggleSaveRecommendation, type RecommendationItem } from '../lib/api'
+import { getRecommendationHistory, getSavedRecommendations, toggleSaveRecommendation, exportSaved, type RecommendationItem } from '../lib/api'
 import RecommendationCard from '../components/RecommendationCard'
 
 type Tab = 'saved' | 'history'
@@ -92,7 +92,18 @@ export default function Recommendations() {
         </div>
       )}
 
-      {/* Tabs */}
+      {/* Export + Tabs */}
+      <div className="flex items-center gap-4">
+        {tab === 'saved' && saved.length > 0 && (
+          <button
+            onClick={() => exportSaved()}
+            className="flex items-center gap-2 px-4 py-2.5 bg-purple-50 text-purple text-sm font-medium rounded-xl hover:bg-purple-100 transition-colors cursor-pointer border-none"
+          >
+            <Download className="w-4 h-4" />
+            Export Saved
+          </button>
+        )}
+      </div>
       <div className="flex gap-1 bg-purple-50 p-1 rounded-xl w-fit">
         <button
           onClick={() => setTab('saved')}