Preview mentions (#5571)

Co-authored-by: Tom Moor <tom.moor@gmail.com>

server/presenters/unfurls/document.ts

@@ -0,0 +1,21 @@
+import { Unfurl, UnfurlType } from "@shared/types";
+import { User, Document } from "@server/models";
+import { presentLastActivityInfoFor } from "./common";
+
+function presentDocument(
+  document: Document,
+  viewer: User
+): Unfurl<UnfurlType.Document> {
+  return {
+    url: document.url,
+    type: UnfurlType.Document,
+    title: document.titleWithDefault,
+    description: presentLastActivityInfoFor(document, viewer),
+    meta: {
+      id: document.id,
+      summary: document.getSummary(),
+    },
+  };
+}
+
+export default presentDocument;