Add comprehensive room management UI:
- CreateRoomModal: Modal for creating new multiplayer rooms
- JoinRoomModal: Modal for joining rooms via code
- JoinRoomInput: Reusable input component for room codes
- PlayOnlineTab: Tab component for arcade lobby
- RecentRoomsList: List of user's recent rooms
- /join/[code] page: Direct join link page
- E2E test for join flow
Includes shareable room links, clipboard integration,
and user-friendly error handling.
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Co-Authored-By: Claude <noreply@anthropic.com>
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