refactor(web): match the media player stand-in to the pipeline's props

The pipeline workstream's MediaPlayer takes artifactId, kind, name, poster
and size, without a MIME type; the card and the stand-in now use exactly
that, so its file replaces the stand-in without other changes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MRtGG9ARfqqhma3t85Ro2u

apps/web/src/components/media/MediaCard.tsx

@@ -277,7 +277,6 @@ export function MediaCardView({
                 <MediaPlayer
                   artifactId={output.artifactId}
                   kind={output.kind}
-                  mimeType={output.mimeType}
                   name={output.name}
                   posterArtifactId={output.posterArtifactId}
                   width={output.width}

apps/web/src/components/media/MediaPlayer.tsx

@@ -1,20 +1,16 @@
-// Stand-in for B1's media player; replaced by B1's component when its branch is merged.
+// Stand-in for the pipeline workstream's media player (same props); its file replaces this one.
 import { artifactUrl } from "../../lib/artifact-url";
 
-export function MediaPlayer({
-  artifactId,
-  kind,
-  name,
-  posterArtifactId,
-}: {
+export type MediaPlayerProps = {
   artifactId: string;
   kind: "video" | "audio";
-  mimeType: string;
   name: string;
   posterArtifactId?: string;
   width?: number;
   height?: number;
-}) {
+};
+
+export function MediaPlayer({ artifactId, kind, name, posterArtifactId }: MediaPlayerProps) {
   if (kind === "audio") {
     // biome-ignore lint/a11y/useMediaCaption: generated media has no caption track yet.
     return <audio controls preload="metadata" src={artifactUrl(artifactId)} aria-label={name} />;