Add signedInAlertResponse() to handle already-authenticated users issue #161

[JiGzSaw01]

This PR applies fixes originally prepared as a patch. The changes address issues when an already-authenticated user attempts to log in again.

Changes included:

• Adds signedInAlertResponse() to return an empty AjaxResponse with an alert for already-signed-in users.
• Prevents warnings and errors caused by controllers returning boolean instead of a Response.
• Ensures consistent fallback response for authenticated users.

Notes:

• The original patch is not included in this PR, All changes are applied directly to the code.
• Tested locally to verify correct behavior.
• Reference: fixes were originally generated as a patch base from the 1.91 updated module.