Add license headers in most files that missed them

.github/workflows/docs.yaml

@@ -1,10 +1,15 @@
+# Copyright 2025 New Vector Ltd.
+#
+# SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+# Please see LICENSE files in the repository root for full details.
+
 name: Build and deploy the documentation
 
 on:
   push:
-    branches: [ main ]
+    branches: [main]
   pull_request:
-    branches: [ main ]
+    branches: [main]
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}