feat(bookmarks): sort & group saved messages by room

The Saved Messages panel showed bookmarks in one fixed order (newest
save first) with no way to reorganize. Add a Newest / Oldest / By-room
segmented sort control to the panel toolbar. In "By room" mode the list
renders collapsible per-room sections, with groups ordered by their most
recently saved message so active rooms float to the top. The chosen sort
persists across panel opens via a localStorage-backed atom.

Ordering and grouping are pure functions in utils/bookmarks.ts
(sortBookmarks, groupBookmarksByRoom) with deterministic eventId
tie-breaks, covered by bookmarks.test.ts (9 tests). No change to the
bookmark data model, account-data schema, useBookmarks, or how bookmarks
are created; search still feeds the sorter/grouper unchanged.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

LOTUS_FEATURES.md

@@ -727,6 +727,8 @@ Redacted events display "This message has been deleted" along with the redaction
 - Bookmarks are stored in `io.lotus.bookmarks` account data, syncing across all devices
 - Maximum of 500 bookmarked entries
 - `BookmarksPanel.tsx` is a sidebar panel accessible from the navigation rail
+- Live-renders edits/redactions, text search, jump-to-message, and remove
+- **Sort & group**: a Newest / Oldest / By-room segmented control sorts the list; "By room" renders collapsible per-room sections (groups ordered by most-recent save). The chosen sort persists across panel opens (`cinny_bookmarks_sort_v1`). Ordering/grouping logic is pure and unit-tested in `src/app/utils/bookmarks.ts` (`bookmarks.test.ts`).
 - Hook: `src/app/hooks/useBookmarks.ts`
 
 ### Message Scheduling