chore: update CLICKZETTA_WORKSPACE default value to quick_start

- Set default workspace to quick_start for better user experience
- Update both docker/.env.example and docker/docker-compose.yaml

🤖 Generated with [Claude Code](https://claude.ai/code)

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

docker/.env.example

@@ -639,7 +639,7 @@ CLICKZETTA_USERNAME=
 CLICKZETTA_PASSWORD=
 CLICKZETTA_INSTANCE=
 CLICKZETTA_SERVICE=api.clickzetta.com
-CLICKZETTA_WORKSPACE=
+CLICKZETTA_WORKSPACE=quick_start
 CLICKZETTA_VCLUSTER=default_ap
 CLICKZETTA_SCHEMA=dify
 CLICKZETTA_BATCH_SIZE=100