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/FileStorageService.cs

@@ -0,0 +1,46 @@
+namespace EchoHub.Server.Services;
+
+public class FileStorageService
+{
+    private readonly string _storagePath;
+
+    public FileStorageService(IConfiguration configuration)
+    {
+        _storagePath = configuration["Storage:Path"] ?? "./uploads";
+
+        if (!Directory.Exists(_storagePath))
+        {
+            Directory.CreateDirectory(_storagePath);
+        }
+    }
+
+    public async Task<(string fileId, string filePath)> SaveFileAsync(Stream stream, string fileName)
+    {
+        var fileId = Guid.NewGuid().ToString();
+        var extension = Path.GetExtension(fileName);
+        var storedFileName = $"{fileId}{extension}";
+        var filePath = Path.Combine(_storagePath, storedFileName);
+
+        using var fileStream = File.Create(filePath);
+        await stream.CopyToAsync(fileStream);
+
+        return (fileId, filePath);
+    }
+
+    public string? GetFilePath(string fileId)
+    {
+        var files = Directory.GetFiles(_storagePath, $"{fileId}.*");
+
+        return files.Length > 0 ? files[0] : null;
+    }
+
+    public void DeleteFile(string fileId)
+    {
+        var filePath = GetFilePath(fileId);
+
+        if (filePath is not null && File.Exists(filePath))
+        {
+            File.Delete(filePath);
+        }
+    }
+}