feat: add Vite configuration for Tiku.PlatformAdmin.Web and update documentation

- Introduced Vite configuration files (vite.config.js, vite.config.ts, vite.config.d.ts) for the React frontend.
- Configured server proxy settings for API endpoints.
- Added Vitest configuration files (vitest.config.js, vitest.config.ts, vitest.config.d.ts) for testing.
- Updated architecture overview to reflect the separation of the platform admin frontend into its own React project.
- Modified quickstart documentation to guide users on starting the platform admin frontend.

docs/quickstart.md

@@ -81,7 +81,7 @@ dotnet run --project Tiku.Api
 
 默认 Development 入口：
 
-- 平台管理端：<http://localhost:5090/platform-admin/>
+- 平台管理端：首次在 `Tiku.PlatformAdmin.Web` 执行 `npm install`；之后启动 `Tiku.Api` 时会在 Development 自动启动前端，访问 <http://localhost:5173>
 - Scalar：<http://localhost:5090/scalar/v1>
 - OpenAPI JSON：<http://localhost:5090/openapi/v1.json>
 - Liveness：<http://localhost:5090/api/health>