chore: add package-lock.json for CI compatibility

Update .gitignore to allow package-lock.json files as they are required
for GitHub Actions CI to pass properly.

Author: pmerrison

.gitignore

@@ -11,10 +11,8 @@ website/node_modules/
 # Generated docs
 docs/contributing.md
 
-# We use YARN
-website/package-lock.json
-package-lock.json
-experimental/calm-explorer/package-lock.json
+# We use YARN (but also need package-lock.json for CI)
+# website/package-lock.json
 /.idea/
 
 **/.vscode/