add audio features too add song route

backend/src/main/java/com/serena/backend/model/Song.java

@@ -1,17 +1,31 @@
 package com.serena.backend.model;
 
+import java.util.Map;
+import java.util.HashMap;
+
 public class Song {
   private String id;
   private int popularity;
+  private double tempo;
+  private Map<String, Double> audioFeatures;
 
-  public Song() {}
+  public Song() {
+    this.audioFeatures = new HashMap<>();
+  }
 
   public Song(String id, int popularity) {
     this.id = id;
     this.popularity = popularity;
+    this.audioFeatures = new HashMap<>();
+  }
+
+  public Song(String id, int popularity, double tempo, Map<String, Double> audioFeatures) {
+    this.id = id;
+    this.popularity = popularity;
+    this.tempo = tempo;
+    this.audioFeatures = audioFeatures != null ? audioFeatures : new HashMap<>();
   }
 
-  // Getters and Setters
   public String getId() {
     return id;
   }
@@ -27,4 +41,20 @@ public class Song {
   public void setPopularity(int popularity) {
     this.popularity = popularity;
   }
+
+  public double getTempo() {
+    return tempo;
+  }
+
+  public void setTempo(double tempo) {
+    this.tempo = tempo;
+  }
+
+  public Map<String, Double> getAudioFeatures() {
+    return audioFeatures;
+  }
+
+  public void setAudioFeatures(Map<String, Double> audioFeatures) {
+    this.audioFeatures = audioFeatures;
+  }
 }

backend/src/main/java/com/serena/backend/service/RadioStationService.java

@@ -38,11 +38,6 @@ public class RadioStationService {
     return new ArrayList<>(radioStations.values());
   }
 
-  public List<RadioStation> getActiveRadioStations() {
-    return radioStations.values().stream()
-        .toList();
-  }
-
   public Optional<RadioStation> updateRadioStation(String stationId, String name, String description) {
     RadioStation station = radioStations.get(stationId);
     if (station != null) {