feat: add destination page configurable modules

This commit adds full support for two new destination page modules: a hero banner section and categorized destination regions.

Changes include:
- New SQLAlchemy models and alembic migration for DestinationHero and DestinationRegion tables
- Updated Pydantic SiteConfigPatchIn schema with new optional fields
- Integrated admin CRUD support for the new modules
- Added default seed data for Guizhou destination regions and hero content
- Exposed active modules via public site config API
- Added comprehensive test coverage for admin and public endpoints

app/schemas.py

@@ -126,6 +126,8 @@ class SiteConfigPatchIn(BaseModel):
     slug: str | None = None
     region: str | None = None
     label: str | None = None
+    keyword: str | None = None
+    spots: str | None = None
     alt: str | None = None
     image: str | None = None
     description: str | None = None