feat(playlists): hybrid table over the drag list, and guard its destructive paths

The column sort and the filters are a VIEW; the playlist's stored order only
changes when the user presses "Save this order", which still goes through the
undoable path. Picking a sort used to write straight to the server, so merely
looking at the list by title rewrote the playlist and marked a YouTube-linked
mirror dirty.

The table:
- playlistColumns.tsx holds the column defs; the body renders them as table rows
  and fills the grip cell itself, since the handle needs the row's sortable
  listeners that a render closure can't reach.
- The # column shows the STORED position, so a view-sort never renumbers the
  playlist under the reader.
- Saving is withheld while a filter is active (it would drop the hidden items),
  and drag is disabled under any view, with the reason spelled out rather than
  silently doing nothing.
- applyView/sameOrder live in lib/playlistView.ts with tests: the sort and the
  channel grouping compose, and getting that wrong produces a plausible order
  that the save button would then persist.
- dnd-kit KeyboardSensor: the grip was focusable and called itself "reorder",
  but only a pointer could move it.

The guards:
- Delete is ONE dialog with every outcome. It was two chained confirms where the
  second one's Cancel/Escape/backdrop meant "delete here only" — dismissing the
  dialog deleted the playlist. ConfirmProvider gained useChoice() for it.
- ConfirmProvider focuses Cancel when an offered action is destructive; the
  confirm button took autoFocus unconditionally, so a stray Enter on an open
  dialog ran "Delete user" or "Clear audit log".
- Removing an item asks first, and rebases the undo history instead of throwing
  it away: useUndoable.rebase maps every snapshot, so the reorder history stays
  valid for the remaining items.
- A failed detail query showed "Loading…" forever; it now says so and offers a
  retry. Rename and reorder failures are surfaced instead of swallowed (reorder
  was a bare .then(), which also produced an unhandled rejection).
- Local reorder/remove no longer require YouTube write scope.
- playlistName() replaces the watch-later localizer copied into three files.

frontend/src/components/PlaylistsRail.tsx

@@ -12,6 +12,7 @@ import SidePanel from "./SidePanel";
 import PanelGroups, { type PanelItem } from "./PanelGroups";
 import { usePlaylists, usePlaylistsActions } from "./PlaylistsProvider";
 import { useMe } from "../lib/useMe";
+import { playlistName } from "../lib/playlistName";
 
 type PlSort = { key: "custom" | "name" | "count" | "duration"; dir: "asc" | "desc"; dirtyFirst: boolean };
 const PL_SORT_DEFAULT: PlSort = { key: "custom", dir: "asc", dirtyFirst: false };
@@ -69,8 +70,7 @@ export default function PlaylistsRail({
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [playlists, selectedId, listQuery.data]);
 
-  const plName = (p: { kind: string; name: string }) =>
-    p.kind === "watch_later" ? t("playlists.watchLater") : p.name;
+  const plName = (p: { kind: string; name: string }) => playlistName(p, t);
 
   const sortedPlaylists = useMemo(() => {
     const sign = plSort.dir === "asc" ? 1 : -1;