feat(smartplaylist): materialize on creation and show track counts

Smart playlists now evaluate and snapshot their rules at creation time
instead of only lazily on first open, so the playlist list can show a
real track count in place of the "Smart" label. A one-time idempotent
startup sweep backfills snapshots for smart playlists created before
creation-time materialization existed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/components/playlist-view/playlist-view.ts

@@ -1930,9 +1930,7 @@ export class PlaylistView extends LitElement {
         index: number,
     ) {
         const trackCount = entry.tracks.length;
-        const countLabel = entry.summary.IsSmart
-            ? 'Smart'
-            : `${trackCount} track${trackCount !== 1 ? 's' : ''}`;
+        const countLabel = `${trackCount} track${trackCount !== 1 ? 's' : ''}`;
         const isDragOver =
             this.dragOverPlaylistIndex === index;