fix: register playCount column in backend AllColumnIDs + rename to 'Play Count'

Backend validation rejected 'playCount' as unknown column ID, silently
preventing it from being enabled or persisted. Added ColPlayCount to
the tracklist package's constant list and AllColumnIDs slice.

backend/tracklist/config.go

@@ -33,6 +33,7 @@ const (
 	ColChannels    ColumnID = "channels"
 	ColBitrate     ColumnID = "bitrate"
 	ColFileSize    ColumnID = "fileSize"
+	ColPlayCount   ColumnID = "playCount"
 )
 
 // AllColumnIDs lists every recognised column in default display
@@ -54,6 +55,7 @@ var AllColumnIDs = []ColumnID{
 	ColChannels,
 	ColBitrate,
 	ColFileSize,
+	ColPlayCount,
 }
 
 // DefaultColumns is the initial column configuration matching the

frontend/src/components/track-list/columns.ts

@@ -188,10 +188,10 @@ export const COLUMN_DEFS: Record<string, ColumnDef> = {
     },
     playCount: {
         id: 'playCount',
-        label: 'Plays',
+        label: 'Play Count',
         accessor: (t) =>
             t.PlayCount ? String(t.PlayCount) : '',
-        defaultWidth: '60px',
+        defaultWidth: '80px',
         align: 'right',
         comparator: (a, b) =>
             compareNum(a.PlayCount, b.PlayCount),