refactor(video-from-script): 提取轮询重试逻辑为共享工具

提取三个视频生成器中重复的 `pollWithRetry` 函数到共享模块 `video-poll-utils`，消除代码重复。新增两层重试机制：轮询级（处理网络瞬断）和任务级（创建新任务 + 提示词优化）。同时优化 `phase-videos` 中视频状态管理和 manifest 保存逻辑。

.claude/skills/video-from-script/scripts/grok-video-generator.js

@@ -402,57 +402,28 @@ async function batchGenerate(tasks, options = {}) {
   return results
 }
 
-/**
- * 轮询 + 失败重试（单任务）
- */
+const { makePollWithRetry } = require('./lib/video-poll-utils')
+
+const pollWithRetryBase = makePollWithRetry({
+  Api: GrokApi,
+  suffix: '_grok',
+  duration: 6,
+  maxRetries: Config.maxRetries,
+  optimizePrompt: (prompt, failReason, attempt) => PromptOptimizer.optimize(prompt, failReason, attempt),
+  buildCreateOpts: (options) => ({ aspectRatio: options.aspectRatio, size: options.size }),
+})
+
 async function pollWithRetry(taskId, prompt, options = {}) {
-  let currentTaskId = taskId
-  let currentPrompt = prompt
-  let lastError = null
+  const result = await pollWithRetryBase(taskId, prompt, options)
 
-  for (let attempt = 0; attempt <= Config.maxRetries; attempt++) {
-    try {
-      if (attempt > 0) {
-        currentPrompt = PromptOptimizer.optimize(prompt, lastError, attempt)
-        console.log(`\n   🔄 重试 (任务 ${currentTaskId.substring(0, 8)}...): ${currentPrompt.substring(0, 50)}`)
-        currentTaskId = await GrokApi.create(
-          options.imageUrl || '',
-          currentPrompt,
-          { aspectRatio: options.aspectRatio, size: options.size }
-        )
-      }
-
-      const result = await GrokApi.poll(currentTaskId)
-
-      const timestamp = new Date().toISOString().replace(/[:.]/g, '-')
-      const videoFile = path.join(options.outputDir || './output', `${timestamp}_grok.mp4`)
-      await download(result.videoUrl, videoFile)
-
-      let thumbnailFile = null
-      if (result.thumbnailUrl) {
-        thumbnailFile = path.join(options.outputDir || './output', `${timestamp}_thumb.jpg`)
-        try { await download(result.thumbnailUrl, thumbnailFile) } catch (_) {}
-      }
-
-      return {
-        taskId: currentTaskId,
-        prompt: currentPrompt,
-        originalPrompt: prompt,
-        attempts: attempt + 1,
-        file: videoFile,
-        files: [videoFile],
-        duration: 6,
-        thumbnail: thumbnailFile,
-      }
-    } catch (err) {
-      lastError = err.message
-      if (attempt < Config.maxRetries) {
-        await new Promise(r => setTimeout(r, 5000))
-      }
-    }
+  let thumbnailFile = null
+  if (result.thumbnailUrl) {
+    const timestamp = new Date().toISOString().replace(/[:.]/g, '-')
+    thumbnailFile = path.join(options.outputDir || './output', `${timestamp}_thumb.jpg`)
+    try { await download(result.thumbnailUrl, thumbnailFile) } catch (_) {}
   }
 
-  throw new Error(`重试 ${Config.maxRetries} 次后仍失败: ${lastError}`)
+  return { ...result, thumbnail: thumbnailFile }
 }
 
 // ============================================================================