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.Client/Themes/Theme.cs

@@ -0,0 +1,18 @@
+namespace EchoHub.Client.Themes;
+
+public class Theme
+{
+    public required string Name { get; set; }
+    public ThemeColors Base { get; set; } = new();
+    public ThemeColors Menu { get; set; } = new();
+    public ThemeColors Dialog { get; set; } = new();
+    public ThemeColors Status { get; set; } = new();
+}
+
+public class ThemeColors
+{
+    public string Foreground { get; set; } = "White";
+    public string Background { get; set; } = "Black";
+    public string FocusForeground { get; set; } = "White";
+    public string FocusBackground { get; set; } = "Blue";
+}