feat: keep every frame in animated avatar thumbnails and raise the thumbnail limit to 800k chars [CI]

server/src/WebDrop.Core/AvatarData.cs

@@ -12,7 +12,7 @@ public static class AvatarData
 
     /// <summary>缩略图(列表、聊天里默认分发的有损小图)的上限:静态约 75 KB,动图约 370 KB</summary>
     public const int MaxThumbStaticChars = 100_000;
-    public const int MaxThumbGifChars = 500_000;
+    public const int MaxThumbGifChars = 800_000;
 
     private static readonly string[] Prefixes = ["data:image/png;base64,", "data:image/jpeg;base64,", "data:image/webp;base64,", "data:image/gif;base64,"];