feat(playlists): act on the selected rows from the toolbar, and undo either

While rows are selected the toolbar's second row is the band: the count,
the last target as one click, Move to, Remove, Clear selection. Both write
in one request and undo back to the places; a video the target held before
stays there. Delete takes the selection when there is one. A failure puts
the rows back ticked.

A row's own move goes through the same write, so it undoes too, and the
single-row move route and service function are gone. A playlist row drops
its grip below a 24rem table: the row menu keeps the moves.

frontend/src/lib/tableColumns.ts

@@ -51,6 +51,9 @@ export interface Column<T> {
   // one beside a panel: a secondary column that gives its room back to the name (the owner,
   // 2026-09-27: at 1024 the channel name had 60 px while About took as much). Same `@container` rule.
   tabletHidden?: boolean;
+  // …and one it leaves out while it is narrower than 24rem, a phone beside the nav rail: there the
+  // title kept 44 px. Only for a column whose job has another way (the grip: the row menu's moves).
+  phoneHidden?: boolean;
 }
 
 // The classes that hide a column below its width (`narrowHidden` / `tabletHidden`), for its cells and,
@@ -71,14 +74,20 @@ const HIDE_BELOW = {
     col: " hidden @5xl:table-column",
     cue: " @5xl:hidden",
   },
+  phone: {
+    cell: " hidden @sm:table-cell",
+    col: " hidden @sm:table-column",
+    cue: " @sm:hidden",
+  },
 } as const;
 
 export function columnHideClass(
-  col: { narrowHidden?: boolean; tabletHidden?: boolean },
+  col: { narrowHidden?: boolean; tabletHidden?: boolean; phoneHidden?: boolean },
   part: "cell" | "col" | "cue" = "cell",
 ): string {
   if (col.narrowHidden) return HIDE_BELOW.narrow[part];
   if (col.tabletHidden) return HIDE_BELOW.tablet[part];
+  if (col.phoneHidden) return HIDE_BELOW.phone[part];
   return "";
 }