fix: SMTP form shows incorrect rate limit message when already enabled (#43914)

## Description

Fixes #43800

When editing SMTP settings while custom SMTP is already enabled, the
form footer was incorrectly displaying "Rate limit for sending emails
will be increased to 30". The rate limit is only set during the initial
enable transition, so the message and submit behavior were out of sync.

## Changes

This fix aligns the footer message with the submit logic (Option A from
the issue):

- **Enabling SMTP**: Shows rate limit increase message
- **Already enabled, editing settings**: Shows "Custom SMTP settings
will be updated"
- **Disabling SMTP**: Shows rate limit reduction message

## Testing

1. Go to Authentication → SMTP Settings
2. Enable custom SMTP and save (rate limit is set to 30)
3. Edit any SMTP field (e.g. change host or port)
4. Footer now correctly shows "Custom SMTP settings will be updated"
instead of the rate limit message

Made with [Cursor](https://cursor.com)

---------

Co-authored-by: vj2303 <vishnu.jangid@ax-ia.ai>
Co-authored-by: Danny White <3104761+dnywh@users.noreply.github.com>

apps/studio/components/interfaces/Auth/SmtpForm/SmtpForm.tsx

@@ -216,6 +216,9 @@ export const SmtpForm = () => {
     )
   }
 
+  const showFooterMessage =
+    form.formState.isDirty && ((enableSmtp && !isSmtpEnabled(authConfig)) || !enableSmtp)
+
   return (
     <PageSection>
       <PageSectionContent>
@@ -462,26 +465,22 @@ export const SmtpForm = () => {
               )}
 
               <CardFooter
-                className={cn(
-                  form.formState.isDirty ? 'justify-between' : 'justify-end',
-                  'gap-x-2'
-                )}
+                className={cn(showFooterMessage ? 'justify-between' : 'justify-end', 'gap-x-2')}
               >
-                {form.formState.isDirty && (
-                  <p className="text-sm text-foreground-light">
-                    {enableSmtp ? (
-                      <>
-                        Rate limit for sending emails will be increased to 30 and{' '}
-                        <InlineLink href={`/project/${projectRef}/auth/rate-limits`}>
-                          can be adjusted
-                        </InlineLink>{' '}
-                        after enabling custom SMTP
-                      </>
-                    ) : (
-                      'Rate limit for sending emails will be reduced to 2 after disabling custom SMTP'
-                    )}
-                  </p>
-                )}
+                {showFooterMessage &&
+                  (enableSmtp ? (
+                    <p className="text-sm text-foreground-light">
+                      Rate limit for sending emails will be increased to 30 and{' '}
+                      <InlineLink href={`/project/${projectRef}/auth/rate-limits`}>
+                        can be adjusted
+                      </InlineLink>{' '}
+                      after enabling custom SMTP
+                    </p>
+                  ) : (
+                    <p className="text-sm text-foreground-light">
+                      Rate limit for sending emails will be reduced to 2 after disabling custom SMTP
+                    </p>
+                  ))}
                 <div className="flex items-center gap-x-2">
                   {form.formState.isDirty && (
                     <Button