Checklist

• Have you pulled and found the error with jc21/nginx-proxy-manager:latest docker image?
  • Yes
• Are you sure you're not using someone else's docker image?
  • Yes
• Have you searched for similar issues (both open and closed)?
  • Yes ( part of the issue being reported here is already reported in this ticket - Unable to setup any Redirection Host #4080 )

Describe the bug
When creating a redirect host using the API endpoint api/nginx/redirection-hosts with "forward_scheme": "auto", the redirect results in a broken URL like auto://google.com. This is not a valid scheme and causes the redirect to fail.

Additionally, when attempting to set "auto" as the scheme in the web UI, the following validation error is shown: data/forward_scheme must be equal to one of the allowed values

This reveals inconsistent behavior:

• The API accepts "auto" but results in a broken redirect.
• The UI correctly rejects "auto" as invalid although it is an option in the form.

Nginx Proxy Manager Version
v2.12.6

To Reproduce
- Using the REST API:

1. Send a POST request to /api/nginx/redirection-hosts with the following JSON payload:

   {
     "domain_names": ["mydomain.com"],
     "forward_scheme": "auto",
     "forward_domain_name": "google.com",
     "forward_http_code": 300,
     "preserve_path": true
   } 

2. Access http://mydomain.com in a browser.
3. Observe that the redirect attempts to go to auto://google.com.

- Using the UI:

1. Open the Nginx Proxy Manager web UI.
2. Go to the "Redirect Hosts" section and click "Add Redirection Host".
3. Fill in domain and forward details.
4. Set Scheme = auto.
5. Try to save.
6. See the following error: data/forward_scheme must be equal to one of the allowed values

Expected behavior

1. If "auto" is intended to be a supported scheme, the redirect should dynamically use the original request's scheme (http or https).
2. If "auto" is not a supported value, it should be rejected consistently across both the API and UI with a validation error.

Additional context
A related issue (#4080) covers the UI validation problem, but this report also includes the API behavior and resulting redirect failure.