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/api/scriptEvalClient.ts

@@ -8,7 +8,6 @@ export interface ScriptEvalResult {
   suggestions: string[];
 }
 
-const DASHSCOPE_API_KEY = import.meta.env.VITE_DASHSCOPE_API_KEY || "";
 const DASHSCOPE_ENDPOINT = "/dashscope-api/chat/completions";
 const MODEL = "qwen3.7-max";
 
@@ -69,15 +68,10 @@ function extractJson(text: string): unknown {
 }
 
 export async function evaluateScript(script: string, signal?: AbortSignal): Promise<ScriptEvalResult> {
-  if (!DASHSCOPE_API_KEY) {
-    throw new Error("DashScope API key 未配置，请在 .env.local 中设置 VITE_DASHSCOPE_API_KEY");
-  }
-
   const res = await fetch(DASHSCOPE_ENDPOINT, {
     method: "POST",
     headers: {
       "Content-Type": "application/json",
-      Authorization: `Bearer ${DASHSCOPE_API_KEY}`,
     },
     body: JSON.stringify({
       model: MODEL,