Add bidirectional Genre relationship to Album entity

This commit extends the Album entity with bidirectional relationship
  management for the AlbumHasGenre join table, enabling many-to-many
  associations between albums and genres with convenient helper methods.

  Key enhancements:

  Relationship Mapping:
  - Added OneToMany relationship from Album to AlbumHasGenre
    * Bidirectional mapping with cascade ALL and orphan removal
    * Maintains collection of album-genre associations
    * Initialized as ArrayList to prevent null pointer exceptions
    * Follows the same pattern as albumArtists relationship

  Helper Methods for Genre Management:
  - addGenre(Genre genre):
    * Creates AlbumHasGenre join table entry
    * Sets bidirectional references to Album and Genre
    * Adds association to albumGenres collection
    * Simplifies adding genres to albums programmatically

  - removeGenre(Genre genre):
    * Removes association by comparing genre IDs
    * Safely handles null checks
    * Uses removeIf for clean collection manipulation
    * Maintains referential integrity

  - getGenres():
    * Convenience method to extract Genre list from join table
    * Uses Java streams for clean transformation
    * Maps AlbumHasGenre → Genre
    * Returns List<Genre> for easy consumption

  Collection Management:
  - Added getAlbumGenres() getter
    * Returns full List<AlbumHasGenre> for direct access
    * Useful for repository-level operations

  - Added setAlbumGenres() setter
    * Allows bulk replacement of genre associations
    * Required by JPA for entity hydration

  Benefits:
  - Enables navigating from Album to associated Genres
  - Simplifies genre association management in service layer
  - Cascade operations ensure join table entries are managed automatically
  - Orphan removal prevents orphaned join table entries
  - Consistent API with existing Artist relationship methods
  - Type-safe genre management through helper methods

  Pattern Consistency:
  This implementation mirrors the albumArtists relationship structure,
  providing a consistent API for managing both artist and genre associations
  on the Album entity. Both relationships use the same cascade and orphan
  removal strategies for reliable data integrity.

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

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

  This commit message is ready to use in IntelliJ for the Album.java changes!

src/main/java/com/mediamanager/model/Album.java

@@ -41,6 +41,10 @@ public class Album {
     @OneToMany(mappedBy = "album", cascade = CascadeType.ALL, orphanRemoval = true)
     private List<AlbumHasArtist> albumArtists = new ArrayList<>();
 
+    // Relacionamento ManyToMany com Genre através da tabela de junção
+    @OneToMany(mappedBy = "album", cascade = CascadeType.ALL, orphanRemoval = true)
+    private List<AlbumHasGenre> albumGenres = new ArrayList<>();  // ← ADICIONE ESSA LINHA
+
     @Column(name = "created_at", nullable = false, updatable = false)
     private LocalDateTime createdAt;
 
@@ -81,6 +85,31 @@ public class Album {
                 .collect(Collectors.toList());
     }
 
+    // ========== ADICIONE ESSES MÉTODOS PARA GENRE ==========
+
+    // Métodos helper para Genre (ManyToMany)
+    public void addGenre(Genre genre) {
+        AlbumHasGenre albumHasGenre = new AlbumHasGenre();
+        albumHasGenre.setAlbum(this);
+        albumHasGenre.setGenre(genre);
+        albumGenres.add(albumHasGenre);
+    }
+
+    public void removeGenre(Genre genre) {
+        albumGenres.removeIf(ag ->
+                ag.getGenre() != null && ag.getGenre().getId().equals(genre.getId())
+        );
+    }
+
+    // Método conveniente para pegar só os gêneros
+    public List<Genre> getGenres() {
+        return albumGenres.stream()
+                .map(AlbumHasGenre::getGenre)
+                .collect(Collectors.toList());
+    }
+
+    // ========== FIM DOS MÉTODOS DE GENRE ==========
+
     // Getters and Setters
     public Integer getId() {
         return id;
@@ -154,6 +183,18 @@ public class Album {
         this.albumArtists = albumArtists;
     }
 
+    // ========== ADICIONE ESSES GETTERS/SETTERS ==========
+
+    public List<AlbumHasGenre> getAlbumGenres() {
+        return albumGenres;
+    }
+
+    public void setAlbumGenres(List<AlbumHasGenre> albumGenres) {
+        this.albumGenres = albumGenres;
+    }
+
+    // ========== FIM DOS GETTERS/SETTERS DE GENRE ==========
+
     public LocalDateTime getCreatedAt() {
         return createdAt;
     }