Add a sort toolbar to the Playlists page: Title A-Z/Z-A, shortest/longest first,
and a 'group by channel' toggle that groups items by channel (A-Z) and applies the
chosen sort within each group. Applying a sort reorders the items and persists via
the existing reorder API.
The item order is now an undoable value: drag, sort and grouping all go through it,
so every change is reversible via undo/redo buttons and Ctrl/Cmd+Z / Ctrl+Y
(Ctrl+Shift+Z). Built on two reusable pieces, not playlist-specific:
- useUndoable<T> — a generic past/present/future snapshot hook (set/undo/redo/reset
+ canUndo/canRedo), ref-backed so callbacks are stable and never see a stale snapshot;
onApply runs the side effect (here: persist order).
- UndoToolbar — undo/redo buttons + keyboard shortcuts, plain props so any undo
source can use it.
Undo history is reset only when the item set actually changes (different playlist or
add/remove), so a refetch confirming our own reorder doesn't wipe it; membership
changes (remove) clear history since they aren't reorder-undoable. Trilingual.
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