perf(canvas): 画布媒体 - 优化媒体加载、播放器与节点交互 (#357)

Merge origin/main at fb089b2 and retain canvas media performance, player layout, and interaction updates.

Co-authored-by: ddCat <2695092045@qq.com>

web/src/lib/canvas/canvas-media-preview.ts

@@ -0,0 +1,23 @@
+import { buildLibTVVideoPreviewUrl } from "@/lib/canvas/libtv-import";
+import { CanvasNodeType, type CanvasNodeData } from "@/types/canvas";
+
+/**
+ * Returns an image source that is safe to mount for a passive video preview.
+ * The original video URL is deliberately never returned: callers must fall
+ * back to a video icon instead of creating a decoder outside the active node.
+ */
+export function canvasNodeVideoPreviewUrl(node: CanvasNodeData) {
+    if (node.type !== CanvasNodeType.Video) return "";
+    const content = node.metadata?.content || "";
+    const generatedPreview = node.metadata?.videoPreview?.content || "";
+    if (generatedPreview && generatedPreview !== content) return generatedPreview;
+    const explicitPreview = node.metadata?.previewContent || "";
+    if (explicitPreview && explicitPreview !== content) return explicitPreview;
+    return buildLibTVVideoPreviewUrl(content);
+}
+
+export function canvasVideoAssetPreviewUrl(videoUrl: string, coverUrl?: string) {
+    const explicitCover = coverUrl?.trim() || "";
+    if (explicitCover && explicitCover !== videoUrl) return explicitCover;
+    return buildLibTVVideoPreviewUrl(videoUrl);
+}