feat: 视频流程树动态节点、全自动流水线、图片/视频点击放大预览

- 一键策划后自动连续执行完整流程（策划→图片→视频），无需手动点继续
- 节点数量跟随 API 返回的分镜数动态生成，策划前只显示 1 个占位节点
- 分镜图片和视频可点击弹出全屏预览浮层

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

src/styles/pages/ecommerce-video.css

@@ -1101,3 +1101,47 @@
   70% { opacity: 0.5; }
   100% { opacity: 0; transform: translateX(100%); }
 }
+
+/* ── Preview lightbox overlay ────────────────────── */
+.ecom-video-preview-overlay {
+  position: fixed;
+  inset: 0;
+  z-index: 9999;
+  display: grid;
+  place-items: center;
+  background: rgba(0, 0, 0, 0.85);
+  backdrop-filter: blur(8px);
+  cursor: zoom-out;
+  animation: ecom-preview-fade-in 200ms ease;
+}
+
+.ecom-video-preview-overlay__close {
+  position: absolute;
+  top: 24px;
+  right: 24px;
+  z-index: 10;
+  display: grid;
+  width: 40px;
+  height: 40px;
+  place-items: center;
+  border: 1px solid rgba(255, 255, 255, 0.2);
+  border-radius: 999px;
+  background: rgba(0, 0, 0, 0.6);
+  color: #fff;
+  font-size: 18px;
+  cursor: pointer;
+}
+
+.ecom-video-preview-overlay img,
+.ecom-video-preview-overlay video {
+  max-width: 90vw;
+  max-height: 85vh;
+  border-radius: 8px;
+  object-fit: contain;
+  cursor: default;
+}
+
+@keyframes ecom-preview-fade-in {
+  from { opacity: 0; }
+  to { opacity: 1; }
+}