Use DTOs to return API requests instead of Database Schema types.

Make use of IHttpStatusCodeResults

API/Controllers/DTOs/Chapter.cs

@@ -0,0 +1,52 @@
+using System.ComponentModel;
+using System.ComponentModel.DataAnnotations;
+
+namespace API.Controllers.DTOs;
+
+/// <summary>
+/// <see cref="API.Schema.MangaContext.Chapter"/> DTO
+/// </summary>
+public record Chapter(string Key, string MangaId, int? Volume, string ChapterNumber, string? Title, IEnumerable<MangaConnectorId> MangaConnectorIds, bool Downloaded) : Identifiable(Key)
+{
+    /// <summary>
+    /// Identifier of the Manga this Chapter belongs to
+    /// </summary>
+    [Required]
+    [Description("Identifier of the Manga this Chapter belongs to")]
+    public string MangaId { get; init; } = MangaId;
+    
+    /// <summary>
+    /// Volume number
+    /// </summary>
+    [Required]
+    [Description("Volume number")]
+    public int? Volume { get; init; } = Volume;
+    
+    /// <summary>
+    /// Chapter number
+    /// </summary>
+    [Required]
+    [Description("Chapter number")]
+    public string ChapterNumber { get; init; } = ChapterNumber;
+    
+    /// <summary>
+    /// Title of the Chapter
+    /// </summary>
+    [Required]
+    [Description("Title of the Chapter")]
+    public string? Title { get; init; } = Title;
+    
+    /// <summary>
+    /// Whether Chapter is Downloaded (on disk)
+    /// </summary>
+    [Required]
+    [Description("Whether Chapter is Downloaded (on disk)")]
+    public bool Downloaded { get; init; } = Downloaded;
+    
+    /// <summary>
+    /// Ids of the Manga on MangaConnectors
+    /// </summary>
+    [Required]
+    [Description("Ids of the Manga on MangaConnectors")]
+    public IEnumerable<MangaConnectorId> MangaConnectorIds { get; init; } = MangaConnectorIds;
+}