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.

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),