fix: also apply width attribute to video block

Apply the same fix as the image block to video:
- React VideoPreview now sets width on the <video> element so read-only
  rendering includes it.
- React VideoToExternalHTML now serializes previewWidth (it was
  previously dropped entirely on export).
- Core video render path guards `video.width = previewWidth` against
  undefined (assigning undefined to a numeric DOM property coerces to
  0).

Audio and File blocks don't have a previewWidth prop, so no change is
needed there.

Refs #2726

Author: nperez0111

packages/core/src/blocks/Video/block.ts

@@ -92,7 +92,9 @@ export const createVideoBlockSpec = createBlockSpec(
       video.controls = true;
       video.contentEditable = "false";
       video.draggable = false;
-      video.width = block.props.previewWidth;
+      if (block.props.previewWidth) {
+        video.width = block.props.previewWidth;
+      }
       videoWrapper.appendChild(video);
 
       return createResizableFileBlockWrapper(

packages/react/src/blocks/Video/block.tsx

@@ -27,6 +27,7 @@ export const VideoPreview = (
           : resolved.downloadUrl
       }
       controls={true}
+      width={props.block.props.previewWidth}
       contentEditable={false}
       draggable={false}
     />
@@ -44,7 +45,7 @@ export const VideoToExternalHTML = (
   }
 
   const video = props.block.props.showPreview ? (
-    <video src={props.block.props.url} />
+    <video src={props.block.props.url} width={props.block.props.previewWidth} />
   ) : (
     <a href={props.block.props.url}>
       {props.block.props.name || props.block.props.url}