fix(security): bookmarks/reminders stop storing decrypted text server-side

For encrypted rooms, bookmarks persist only {roomId, eventId, savedAt}
and reminders only their non-text fields; the preview, room name and
sender resolve locally at render/fire time from the timeline (with a
"Message unavailable" fallback). A one-time, loop-guarded cleanup strips
text from existing entries in currently-encrypted rooms. Unencrypted
rooms are unchanged. Unit-tested.

Fixes #10

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/features/room/message/Message.tsx

@@ -1273,6 +1273,9 @@ export const Message = React.memo(
                                     const content = mEvent.getContent();
                                     const body: string =
                                       (content?.body as string | undefined) ?? '';
+                                    // For E2EE rooms useBookmarks strips the text
+                                    // fields before persisting (account data is
+                                    // server-readable); the panel resolves them live.
                                     addBookmark({
                                       roomId: room.roomId,
                                       eventId,