feat: Add WonderQ-MiniAPP Public API documentation

- Introduced a comprehensive API contract for the WonderQ-MiniAPP, detailing endpoints for site configuration, product listings, and lead submissions.
- Defined data types for various entities including HeroSlide, Destination, Theme, CtaBanner, PublicProduct, and more.
- Specified request and response formats, including error handling guidelines.

chore: Update requirements to include python-multipart

- Added python-multipart dependency to requirements.txt for handling file uploads.

test: Implement API contract tests

- Created test suite for API contracts, validating serializers and endpoints for public products and leads.
- Included tests for destination and product serializers, ensuring correct data handling and validation.

test: Add configuration tests for OSS settings

- Implemented tests to verify that OSS settings are correctly loaded from environment variables.

docs/README.md

@@ -3,6 +3,8 @@
 本目录存放后端 API 相关文档。
 
 - `backend/README.md`：当前 Python + FastAPI 后端运行说明。
+- `admin-ui-api-requirements.md`：后台管理前端当前必需的 Admin API 对接需求与字段契约。
+- `miniapp-public-api.md`：WonderQ-MiniAPP 前台对接 Public API 契约。
 - `admin-backend-plan.md`：早期后台建设规划，保留作业务范围和阶段规划参考；其中技术栈建议已被当前 Python 迁移方案取代。
 
 后台管理前端文档位于 `D:\www\znkj\WonderQ-Admin-UI\docs`。