fix(ecommerce): video 400 error — use OSS URLs instead of data URLs for video generation

The renderScene function was passing local data URLs (data:image/png;base64,...)
as imageUrl and referenceUrls to createVideoTask, which the /api/ai/video endpoint
rejects with 400 Bad Request. The planning phase already uploads images to OSS
but the resulting URLs were not returned to the component.

- Add imageUrls field to EcommerceVideoPlanResult
- Return OSS imageUrls from runVideoPlan alongside existing plan data
- Use planResult.imageUrls[0] in handleRender instead of productImageDataUrls[0]
- Use planResult?.imageUrls[0] for sourceImage display fallback

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

src/features/ecommerce/EcommerceVideoWorkspace.tsx

@@ -170,7 +170,7 @@ export default function EcommerceVideoWorkspace({
 
   const handleRender = async () => {
     if (!planResult || !scenes.length) return;
-    const imageUrl = productImageDataUrls[0] || "";
+    const imageUrl = planResult.imageUrls[0] || "";
     setStage("rendering");
     setError(null);
     renderAbortRef.current = { current: false };
@@ -213,7 +213,7 @@ export default function EcommerceVideoWorkspace({
   const completedScenes = scenes.filter((s) => s.status === "completed" && s.resultUrl);
   const primaryVideo = completedScenes[0]?.resultUrl;
   const canRender = planResult?.compliance.allow_video_generation && stage === "planned";
-  const sourceImage = productImageDataUrls[0] || "";
+  const sourceImage = planResult?.imageUrls[0] || productImageDataUrls[0] || "";
   const flowHasStarted = stage !== "idle" || completedSteps.length > 0 || scenes.length > 0;
   const flowMeta = `${platform} / ${aspectRatio} / ${durationSeconds}s / ${resolution}`;
   const planActionLabel = stage === "planning"