fix(web): pin ReDoc JS to v2.1.3 (cdn redoc@next returns 404)

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

src/easy_tdx/web/app.py

@@ -102,6 +102,7 @@ def _create_app(
         description="通达信行情数据 REST + WebSocket API",
         version="1.0.0",
         lifespan=lifespan,
+        redoc_js_url="https://cdn.jsdelivr.net/npm/redoc@2.1.3/bundles/redoc.standalone.js",
     )
 
     # Store connection config in app.state for lifespan to use