fix(extensions): make LOCAL_EXTENSIONS hot reload reliable in Docker (#40084)

Co-authored-by: Amin Ghadersohi <amin.ghadersohi@gmail.com>
Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

docker-compose.yml

@@ -34,6 +34,7 @@ x-superset-volumes: &superset-volumes
   - superset_home:/app/superset_home
   - ./tests:/app/tests
   - superset_data:/app/data
+  - ./local_extensions:/app/local_extensions
 x-common-build: &common-build
   context: .
   target: ${SUPERSET_BUILD_TARGET:-dev} # can use `dev` (default) or `lean`