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";

src/styles/pages/not-found.css

@@ -0,0 +1,56 @@
+.not-found-page {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  min-height: calc(100vh - 60px);
+  padding: 48px 24px;
+  background: var(--app-bg, #0b0b0f);
+}
+
+.not-found-page__content {
+  text-align: center;
+  max-width: 420px;
+}
+
+.not-found-page__code {
+  font-size: 96px;
+  font-weight: 800;
+  line-height: 1;
+  letter-spacing: -0.03em;
+  color: var(--accent-teal, #2dd4bf);
+  margin-bottom: 12px;
+}
+
+.not-found-page h1 {
+  font-size: 22px;
+  font-weight: 600;
+  color: var(--text-primary, #f1f5f9);
+  margin: 0 0 8px;
+}
+
+.not-found-page p {
+  font-size: 14px;
+  color: var(--text-secondary, #94a3b8);
+  margin: 0 0 28px;
+  line-height: 1.6;
+}
+
+.not-found-page__button {
+  display: inline-flex;
+  align-items: center;
+  gap: 8px;
+  padding: 10px 24px;
+  border: 1px solid var(--border-default, #334155);
+  border-radius: 8px;
+  background: var(--surface-elevated, #1e293b);
+  color: var(--text-primary, #f1f5f9);
+  font-size: 14px;
+  font-weight: 500;
+  cursor: pointer;
+  transition: background 0.2s, border-color 0.2s;
+}
+
+.not-found-page__button:hover {
+  background: var(--surface-hover, #334155);
+  border-color: var(--accent-teal, #2dd4bf);
+}