feat(design): the channel menu's Tags and Priority submenus (C1, E28 S3e3b)

Tags A-Z as in-place checks (the menu stays open for the next); Priority
as the fixed steps 10 5 3 2 1 0, an off-scale current value ticked in its
place. A pick re-sorts the list at once, moving only that row
(placeByPriority, the server's order), and the table / card pager and
the focus follow it (DataTable and useCardPager take a reveal seq,
listNav.focusNavItem lands on the row's own "…", a virtualized card
revealed first). ActionMenu rows take check: many | one. The menu reads
the row fresh from the cache and keys its target by id.

frontend/src/lib/useCardPager.ts

@@ -10,11 +10,26 @@ import { readAccount, writeAccount } from "./storage";
 //
 // The page size persists per account; the page itself is transient. `enabled` is the card layout
 // flag — in table mode DataTable does its own paging, so this does no work and holds still.
-export function useCardPager<T>(rows: T[], sizeKey: string, enabled: boolean) {
+export function useCardPager<T>(
+  rows: T[],
+  sizeKey: string,
+  enabled: boolean,
+  /** Follow a row the caller just moved: each new `seq` turns to the page holding the row `match`
+   *  finds — the same contract as `DataTable`'s `reveal`, for the card paint of the same list. */
+  reveal?: { seq: number; match: (row: T) => boolean } | null,
+) {
   const { t } = useTranslation();
   const [size, setSize] = useState(() => parseCardSize(readAccount(sizeKey, null)));
   const [page, setPage] = useState(0);
 
+  // During render against the last seq seen, as in DataTable (seeded so a mount never jumps).
+  const [revealSeen, setRevealSeen] = useState(reveal?.seq);
+  if (reveal && reveal.seq !== revealSeen) {
+    setRevealSeen(reveal.seq);
+    const at = rows.findIndex(reveal.match);
+    if (enabled && at >= 0 && size > 0) setPage(Math.floor(at / size));
+  }
+
   const totalPages = size <= 0 ? 1 : Math.max(1, Math.ceil(rows.length / size));
   const safePage = Math.min(page, totalPages - 1);