Backend:
- Add reaction_batch handler: GET /api/rooms/{room_id}/messages/reactions/batch?message_ids=...
- Register route in libs/api/room/mod.rs
- Backend already had message_reactions_batch service method, just needed HTTP exposure
Frontend:
- Add ReactionListData import to room-context.tsx
- Fix thisLoadReactions client type (was using broken NonNullable<ReturnType<>>)
- Remove unused oldRoomId variable
- Delete unused useRoomWs.ts hook (RoomWsClient has no on/off methods)
- Remove unused EmojiPicker function and old manual overlay picker from RoomMessageBubble
- Remove unused savedToken variable in room-ws-client
