WinForms QR/Barcode Camera Reader

I need a compact C# WinForms demo: one form, nothing more. When the form loads it should enumerate every camera the laptop sees—both the built-in webcam and any USB external units—then populate a drop-down at the top with those names.

Once the user picks a camera, start a live preview in an image box directly beneath the list. As soon as either a QR code or a traditional 1-D barcode comes into view, decode it immediately. Show the resulting string on the form for a brief moment (a couple of seconds is fine) and then close the form automatically. No additional clicks should be required after the initial camera selection.

Feel free to rely on libraries such as ZXing.Net or any open-source alternative that keeps the project lightweight and royalty-free; just include any NuGet references in the solution. Please deliver:
• Visual Studio solution with clearly commented code
• A short README noting dependencies and how to build/run

If the form launches, lists cameras, previews video, correctly reads both QR and linear barcodes, displays the decoded value, and then shuts itself down, the task is complete.