Refactor annotation tool from WPF desktop app to .NET API

Replace the WPF desktop application (Azaion.Suite, Azaion.Annotator,
Azaion.Common, Azaion.Inference, Azaion.Loader, Azaion.LoaderUI,
Azaion.Dataset, Azaion.Test) with a standalone .NET Web API in src/.

Made-with: Cursor

src/Middleware/ErrorHandlingMiddleware.cs

@@ -0,0 +1,40 @@
+using System.Net;
+using System.Text.Json;
+
+namespace Azaion.Annotations.Middleware;
+
+public class ErrorHandlingMiddleware(RequestDelegate next, ILogger<ErrorHandlingMiddleware> logger)
+{
+    public async Task Invoke(HttpContext context)
+    {
+        try
+        {
+            await next(context);
+        }
+        catch (KeyNotFoundException ex)
+        {
+            await WriteError(context, HttpStatusCode.NotFound, ex.Message);
+        }
+        catch (ArgumentException ex)
+        {
+            await WriteError(context, HttpStatusCode.BadRequest, ex.Message);
+        }
+        catch (InvalidOperationException ex)
+        {
+            await WriteError(context, HttpStatusCode.Conflict, ex.Message);
+        }
+        catch (Exception ex)
+        {
+            logger.LogError(ex, "Unhandled exception");
+            await WriteError(context, HttpStatusCode.InternalServerError, "Internal server error");
+        }
+    }
+
+    private static async Task WriteError(HttpContext context, HttpStatusCode code, string message)
+    {
+        context.Response.StatusCode = (int)code;
+        context.Response.ContentType = "application/json";
+        var body = JsonSerializer.Serialize(new { statusCode = (int)code, message });
+        await context.Response.WriteAsync(body);
+    }
+}