Improve missing repo error message

The new file structure makes it clear that this component is only used
when there is no repo in the URL path.

Author: victorlin

static-site/app/community/[user]/page.tsx

@@ -10,5 +10,5 @@ export default function Page({
     user: string;
   };
 }): React.ReactElement {
-  return <MissingRepoErrorPage />;
+  return <MissingRepoErrorPage user={params.user} />;
 }

static-site/app/community/error-page.tsx

@@ -7,14 +7,18 @@ import CommunityPageContent from "./content";
 import { usePathname } from "next/navigation";
 
 /**
- * Renders a generic error page.
+ * Renders an error page for incomplete user-only paths.
  */
-export function MissingRepoErrorPage(): React.ReactElement {
+export function MissingRepoErrorPage({
+  user,
+}: {
+  user: string;
+}): React.ReactElement {
   const errorPath = "nextstrain.org" + usePathname();
   return (
     <>
       <ErrorMessage
-        title={`The community repository, dataset, or narrative "${errorPath}" doesn't exist.`}
+        title={`The path "${errorPath}" is not valid. If you are looking for resources under "${user}", add a repo to the path: "${errorPath}/{repo}"`}
         contents={<p>Here is the community page instead.</p>}
       />
       <CommunityPageContent />

static-site/app/community/narratives/[user]/page.tsx

@@ -10,5 +10,5 @@ export default function Page({
     user: string;
   };
 }): React.ReactElement {
-  return <MissingRepoErrorPage />;
+  return <MissingRepoErrorPage user={params.user} />;
 }