Add a public subscription plan list endpoint that can be accessed without authentication. Enhance the returned subscription plan information fields, including multi-language support and default free plan fallback logic. Additionally, implement automatic model binding for the knowledge base service.
- Add `default_free_plan.py` to define the configuration for the Community Free Plan.
- Refactor `quota_stub.py` as a unified entry point, delegating checks to `core/quota_manager`.
- Implement core logic in `quota_manager.py` to support retrieving quotas from the premium module or configuration files.
- Update `tenant_subscription_controller` to return Community Free Plan information.
