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/components/ui/tableHeader.tsx

@@ -214,7 +214,7 @@ export function ColumnHead<T>({
             <th
               key={col.key}
               style={col.width ? { width: col.width } : undefined}
-              className={`relative font-medium px-2 py-2 whitespace-nowrap bg-bg ${alignClass(col.align)}${col.phoneHidden ? " hidden sm:table-cell" : ""}`}
+              className={`relative font-medium px-2 py-2 whitespace-nowrap bg-bg ${alignClass(col.align)}${col.narrowHidden ? " hidden @2xl:table-cell" : ""}`}
               aria-sort={
                 col.sortable
                   ? isSorted