Add infinite scroll, gone/private tiles, and live-only scrape strip

poc/src/media.ts

@@ -121,6 +121,8 @@ export interface MediaItemResult {
     playUrl: string | null;
     /** The remote thumbnail URL from Discord's embed data (may be an animated GIF). */
     remotePreviewUrl: string | null;
+    /** Why no preview exists, when a fetch failed (for example "http 404"). */
+    previewError: string | null;
     localUrl: string | null;
     thumbUrl: string | null;
     provider: string | null;
@@ -739,6 +741,7 @@ export class MediaService {
                 url: row.url,
                 playUrl: row.play_url,
                 remotePreviewUrl: row.preview_url,
+                previewError: row.preview_error,
                 localUrl:
                     row.file_path && !meta.downloadDir
                         ? `/api/media/${meta.id}/${row.id}/file`