feat(bookmarks): show who wrote each saved message

Saved-message cards showed the room and time but not the author, so in a busy
room you couldn't tell who said it without jumping. Now each card shows
"{sender} - {time ago}":

- Bookmark gains optional senderId/senderName (snapshotted at save time in
  Message.tsx from the already-computed sender display name); optional so
  existing stored bookmarks stay valid.
- The panel re-resolves the author's current display name live from the event
  when the room is joined, falling back to the stored snapshot for left rooms.
- Search now also matches the author name.

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

LOTUS_FEATURES.md

@@ -733,6 +733,7 @@ Redacted events display "This message has been deleted" along with the redaction
 - 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
+- **Author attribution**: each saved-message card shows who wrote it (`{sender} · {time ago}`). The author is snapshotted at save time (`senderId`/`senderName` on the bookmark, optional for backward compatibility) and re-resolved live from the event when the room is joined; search also matches the author name.
 - **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`