chore(docker): enable ENABLE_TEMPLATE_PROCESSING in dev config

Turn on Jinja templating in the docker-compose-light dev image and
Showtime preview environments so the SQL Lab "Template parameters"
popover is reachable for review. The default in `superset/config.py`
stays `False` for production safety; this only affects local dev and
ephemeral preview envs.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docker/pythonpath_dev/superset_config.py

@@ -109,6 +109,7 @@ FEATURE_FLAGS = {
     "ALERT_REPORTS": True,
     "DATASET_FOLDERS": True,
     "ENABLE_EXTENSIONS": True,
+    "ENABLE_TEMPLATE_PROCESSING": True,
     "SEMANTIC_LAYERS": True,
 }
 EXTENSIONS_PATH = "/app/docker/extensions"