feat(server): send mention email (#10859)

close CLOUD-170

packages/backend/server/src/mails/docs/mention.tsx

@@ -0,0 +1,37 @@
+import { TEST_DOC, TEST_USER } from '../common';
+import {
+  Button,
+  Content,
+  Doc,
+  type DocProps,
+  P,
+  Template,
+  Title,
+  User,
+  type UserProps,
+} from '../components';
+
+export type MentionProps = {
+  user: UserProps;
+  doc: DocProps;
+};
+
+export function Mention(props: MentionProps) {
+  const { user, doc } = props;
+  return (
+    <Template>
+      <Title>You are mentioned!</Title>
+      <Content>
+        <P>
+          <User {...user} /> mentioned you in <Doc {...doc} />.
+        </P>
+        <Button href={doc.url}>Open Doc</Button>
+      </Content>
+    </Template>
+  );
+}
+
+Mention.PreviewProps = {
+  user: TEST_USER,
+  doc: TEST_DOC,
+};