feat: add attachment file size support for messages and update upload limits

src/EchoHub.Core/Constants/HubConstants.cs

@@ -6,8 +6,9 @@ public static class HubConstants
     public const string DefaultChannel = "general";
     public const int DefaultHistoryCount = 100;
     public const int MaxMessageLength = 2000;
-    public const int MaxFileSizeBytes = 10 * 1024 * 1024; // 10 MB
-    public const int MaxAudioFileSizeBytes = 20 * 1024 * 1024; // 20 MB
+    public const int MaxImageSizeBytes = 10 * 1024 * 1024; // 10 MB
+    public const int MaxAudioFileSizeBytes = 10 * 1024 * 1024; // 10 MB
+    public const int MaxFileSizeBytes = 100 * 1024 * 1024; // 100 MB
     public const int MaxAvatarSizeBytes = 2 * 1024 * 1024; // 2 MB
     public const int MaxMessageNewlines = 30;
     public const int MaxConsecutiveNewlines = 1;

src/EchoHub.Core/DTOs/ChatDtos.cs

@@ -12,6 +12,7 @@ public record MessageDto(
     string? AttachmentUrl,
     string? AttachmentFileName,
     DateTimeOffset SentAt,
+    long? AttachmentFileSize = null,
     List<EmbedDto>? Embeds = null);
 
 public record ChannelDto(

src/EchoHub.Core/Models/Message.cs

@@ -7,6 +7,7 @@ public class Message
     public MessageType Type { get; set; } = MessageType.Text;
     public string? AttachmentUrl { get; set; }
     public string? AttachmentFileName { get; set; }
+    public long? AttachmentFileSize { get; set; }
     public string? EmbedJson { get; set; }
     public DateTimeOffset SentAt { get; set; } = DateTimeOffset.UtcNow;