Move the form_post auto-submit script to a frontend entrypoint

frontend/src/entrypoints/form-post.ts

@@ -0,0 +1,10 @@
+// Copyright 2026 Element Creations Ltd.
+//
+// SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+// Please see LICENSE files in the repository root for full details.
+
+// Submit the form on the next tick, so the browser can paint the
+// placeholder before navigating away.
+setTimeout(() => {
+  document.forms[0].submit();
+}, 0);

templates/form_post.html

@@ -1,4 +1,5 @@
 {#
+Copyright 2025, 2026 Element Creations Ltd.
 Copyright 2024, 2025 New Vector Ltd.
 Copyright 2021-2024 The Matrix.org Foundation C.I.C.
 
@@ -28,5 +29,5 @@ Please see LICENSE files in the repository root for full details.
 
   {# Submit the form in JavaScript on the next tick, so that if the browser
      wants to display the placeholder instead of a blank page, it can #}
-  <script>setTimeout(function() { document.forms[0].submit(); }, 0);</script>
+  {{ include_asset('src/entrypoints/form-post.ts') | indent(2) | safe }}
 {% endblock %}