fix: Prevent user enumeration on password reset endpoint (#13528)

## Description

The current password reset endpoint returns different HTTP status codes
and messages depending on whether the email exists in the system (200
for existing emails, 404 for non-existing ones). This allows attackers
to enumerate valid email addresses via the password reset form.

## Changes

### `app/controllers/devise_overrides/passwords_controller.rb`
- Removed the `if/else` branch that returned different responses based
on email existence
- Now always returns a generic `200 OK` response with the same message
regardless of whether the email exists
- Uses safe navigation operator (`&.`) to send reset instructions only
if the user exists

### `config/locales/en.yml`
- Consolidated `reset_password_success` and `reset_password_failure`
into a single generic `reset_password` key
- New message does not reveal whether the email exists in the system

## Security Impact
- **Before**: An attacker could determine if an email was registered by
observing the HTTP status code (200 vs 404) and response message
- **After**: All requests receive the same 200 response with a generic
message, preventing user enumeration

This follows [OWASP guidelines for authentication error
messages](https://cheatsheetseries.owasp.org/cheatsheets/Authentication_Cheat_Sheet.html#authentication-responses).

Fixes #13527

config/locales/en.yml

@@ -41,8 +41,7 @@ en:
       invalid_email: 'Please enter a valid email address'
       authentication_failed: 'Authentication failed. Please check your credentials and try again.'
   messages:
-    reset_password_success: Woot! Request for password reset is successful. Check your mail for instructions.
-    reset_password_failure: Uh ho! We could not find any user with the specified email.
+    reset_password: Request for password reset is successful. A email with instructions will be sent to your email if it exists.
     reset_password_saml_user: This account uses SAML authentication. Password reset is not available. Please contact your administrator.
     login_saml_user: This account uses SAML authentication. Please sign in through your organization's SAML provider.
     saml_not_available: SAML authentication is not available in this installation.