chore: import upstream snapshot with attribution

apps/sim/components/emails/auth/existing-account-email.tsx

@@ -0,0 +1,46 @@
+import { Link, Text } from '@react-email/components'
+import { baseStyles } from '@/components/emails/_styles'
+import { EmailLayout } from '@/components/emails/components'
+import { getBaseUrl } from '@/lib/core/utils/urls'
+import { getBrandConfig } from '@/ee/whitelabeling'
+
+interface ExistingAccountEmailProps {
+  username?: string
+}
+
+/**
+ * Sent out-of-band when someone attempts to sign up with an email that already
+ * has an account. The sign-up endpoint itself returns a generic success
+ * response to avoid account enumeration, so this email is how the real account
+ * owner learns of the attempt.
+ */
+export function ExistingAccountEmail({ username = '' }: ExistingAccountEmailProps) {
+  const brand = getBrandConfig()
+  const loginLink = `${getBaseUrl()}/login`
+
+  return (
+    <EmailLayout
+      preview={`Someone tried to sign up with your ${brand.name} email`}
+      showUnsubscribe={false}
+    >
+      <Text style={baseStyles.paragraph}>Hello {username},</Text>
+      <Text style={baseStyles.paragraph}>
+        Someone just tried to create a {brand.name} account using this email address, but an account
+        already exists. If this was you, sign in instead — or reset your password if you've
+        forgotten it.
+      </Text>
+
+      <Link href={loginLink} style={{ textDecoration: 'none' }}>
+        <Text style={baseStyles.button}>Sign In</Text>
+      </Link>
+
+      <div style={baseStyles.divider} />
+
+      <Text style={{ ...baseStyles.footerText, textAlign: 'left' }}>
+        If this wasn't you, no action is needed — no account was created or changed.
+      </Text>
+    </EmailLayout>
+  )
+}
+
+export default ExistingAccountEmail