Implement an image processor server with middleware

1. GET Pass a URL with image with instructions.
2. Get processed image back.

No files, entry points, image-processing library, or tests are named. Start by reviewing the repository's ASP.NET Core samples to identify where a server and middleware belong, then clarify the URL and instruction format, supported processing operations, and expected response. Done means a GET request accepts an image URL and instructions and returns the processed image.

Written by the indexing model from the issue text.