feat(admin): add MP3 validation with detailed audio info and cover detection

app/admin/page.tsx

@@ -84,7 +84,25 @@ export default function AdminPage() {
         });
 
         if (res.ok) {
-            setMessage('Song uploaded successfully!');
+            const data = await res.json();
+            const validation = data.validation;
+
+            let statusMessage = '✅ Song uploaded successfully!\n\n';
+            statusMessage += `📊 Audio Info:\n`;
+            statusMessage += `• Format: ${validation.codec || 'unknown'}\n`;
+            statusMessage += `• Bitrate: ${Math.round(validation.bitrate / 1000)} kbps\n`;
+            statusMessage += `• Sample Rate: ${validation.sampleRate} Hz\n`;
+            statusMessage += `• Duration: ${Math.round(validation.duration)} seconds\n`;
+            statusMessage += `• Cover Art: ${validation.hasCover ? '✅ Yes' : '❌ No'}\n`;
+
+            if (validation.warnings.length > 0) {
+                statusMessage += `\n⚠️ Warnings:\n`;
+                validation.warnings.forEach((warning: string) => {
+                    statusMessage += `• ${warning}\n`;
+                });
+            }
+
+            setMessage(statusMessage);
             setFile(null);
             fetchSongs();
         } else {
@@ -247,7 +265,20 @@ export default function AdminPage() {
                     <button type="submit" className="btn-primary">
                         Upload Song
                     </button>
-                    {message && <p style={{ textAlign: 'center', marginTop: '0.5rem' }}>{message}</p>}
+                    {message && (
+                        <div style={{
+                            marginTop: '1rem',
+                            padding: '1rem',
+                            background: message.includes('⚠️') ? '#fff3cd' : '#d4edda',
+                            border: `1px solid ${message.includes('⚠️') ? '#ffc107' : '#28a745'}`,
+                            borderRadius: '0.25rem',
+                            whiteSpace: 'pre-line',
+                            fontSize: '0.875rem',
+                            fontFamily: 'monospace'
+                        }}>
+                            {message}
+                        </div>
+                    )}
                 </form>
             </div>