feat(track-list): show Album by default, and search smart playlists

H-15: the default columns were track, artist and duration, so a library
manager with duplicate detection could not tell its own duplicate
fixtures apart by eye. Album is a default now, in Go and in the
frontend fallback — both, because a fresh install persists the Go list
and the UI renders the TS one until the config arrives.

It does not deliver the finding's stated benefit, and that is worth
recording: the three `Tideline / Aurora Fields / 00:06` rows are
duplicates of the same album, so they read identically with an Album
column too. What tells them apart is the duplicate-detection feature or
a file path column, not this. Album is still the right default for
every other row in the list.

smart-playlist-details joins search-store's scope map. Checked before
adding, as asked: it reads searchCtrl.term in getVisibleTracks and
prints the term in the page, so the header box was disabled and
unlabelled on a view that filters as you type — the fix is a scope
entry, not a disabled state with a reason.

backend/tracklist/config.go

@@ -60,11 +60,16 @@ var AllColumnIDs = []ColumnID{
 	ColPlayCount,
 }
 
-// DefaultColumns is the initial column configuration matching the
-// original hardcoded layout.
+// DefaultColumns is the initial column configuration.  Album is in it
+// (H-15): without it the three identical `Tideline / Aurora Fields /
+// 00:06` rows in this app's own fixture library cannot be told apart,
+// in an app that has a duplicate-detection feature.  Must match
+// DEFAULT_COLUMN_IDS in frontend/src/components/track-list/columns.ts,
+// which is what the UI falls back to before the config arrives.
 var DefaultColumns = []Column{
 	{ID: ColTrackName},
 	{ID: ColArtistName},
+	{ID: ColAlbum},
 	{ID: ColTrackLength},
 }