fix: 电商视频生成链路稳定性 — AI超时/重试/断点续传 + 404页面 + DashScope Key移除

- adVideoPlanClient: 模型级联降级(qwen-max→plus→turbo), 5xx/网络错误可重试, 超时延长至180s, 错误信息包含上游响应体
- 服务端ai/chat: 超时60s→120s, AbortError返回504(非500), PM2已热重载
- EcommerceVideoWorkspace: 策划失败后支持从断点继续(保留已完成步骤的中间产物), 分镜图/视频生成仅重做失败场景
- scriptEvalClient: 移除客户端DASHSCOPE_API_KEY引用(Nginx代理注入)
- NotFoundPage: 未知路由显示404页面(替代兜底跳首页)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/styles/index.css

@@ -29,6 +29,7 @@
 @import "./pages/compliance.css";
 @import "./pages/provider-health.css";
 @import "./pages/legacy-pages.css";
+@import "./pages/not-found.css";
 @import "./components/recharge-modal.css";
 @import "./components/dropzone.css";
 @import "./components/skeleton.css";