Add core models, DTOs, and services for EchoHub chat application

- Created User, Channel, Message, and ServerInfo models with necessary properties.
- Added DTOs for user profiles, server information, and message handling.
- Implemented JWT authentication service for user login and token generation.
- Developed Entity Framework Core DbContext for database interactions.
- Introduced SignalR ChatHub for real-time messaging and presence tracking.
- Implemented file storage and image to ASCII conversion services.
- Set up CORS and middleware for API endpoints.
- Created launch settings and development configuration for server and web projects.

src/EchoHub.Server/Services/ImageToAsciiService.cs

@@ -0,0 +1,41 @@
+using System.Text;
+using EchoHub.Core.Constants;
+using SixLabors.ImageSharp;
+using SixLabors.ImageSharp.PixelFormats;
+using SixLabors.ImageSharp.Processing;
+
+namespace EchoHub.Server.Services;
+
+public class ImageToAsciiService
+{
+    private static readonly char[] AsciiChars = " .:-=+*#%@".ToCharArray();
+
+    public string ConvertToAscii(Stream imageStream, int width = HubConstants.AsciiArtWidth, int height = HubConstants.AsciiArtHeight)
+    {
+        using var image = Image.Load<Rgba32>(imageStream);
+
+        image.Mutate(x => x.Resize(width, height));
+
+        var sb = new StringBuilder();
+
+        for (int y = 0; y < image.Height; y++)
+        {
+            for (int x = 0; x < image.Width; x++)
+            {
+                var pixel = image[x, y];
+                var brightness = 0.299 * pixel.R + 0.587 * pixel.G + 0.114 * pixel.B;
+
+                // Map brightness (0-255) to ASCII char index (inverted: dark pixels get dense chars)
+                var index = (int)((brightness / 255.0) * (AsciiChars.Length - 1));
+                sb.Append(AsciiChars[index]);
+            }
+
+            if (y < image.Height - 1)
+            {
+                sb.AppendLine();
+            }
+        }
+
+        return sb.ToString();
+    }
+}