fix(playlists): hide '#' and Channel by the table's width, not the window's (E28)

Beside the playlist rail an 800 px window left the table 432 px: the fixed
columns took all of it and the title column was 0 px wide, its thumbnail
drawn over the channel. The table is an @container now and the columns hide
under 42rem of its own width (narrowHidden, was phoneHidden).

frontend/src/lib/tableColumns.ts

@@ -38,8 +38,10 @@ export interface Column<T> {
   hideInCard?: boolean;
   cardLabel?: boolean;
   // A column a table WITHOUT the card fallback (the playlist's drag-reorderable hybrid) leaves out
-  // below `sm`: on a phone its fixed widths alone overran the screen and left the title no width.
-  phoneHidden?: boolean;
+  // while the TABLE is narrower than 42rem: its fixed widths alone overran the box and left the title
+  // no width. The table's own width, not the viewport's (an `@container` round it): beside the
+  // playlist rail a desktop window gave the table 432 px, and the title column was 0 px wide.
+  narrowHidden?: boolean;
 }
 
 export type FilterMap = Record<string, string | string[]>;