CREATE TABLE board_archives (
    id SERIAL PRIMARY KEY,
    user_id INTEGER NOT NULL REFERENCES users(id),
    board_type VARCHAR(20) NOT NULL, -- 'wishlist' or 'shopping'
    board_id INTEGER NOT NULL,
    archived_at TIMESTAMP NOT NULL DEFAULT NOW(),
    UNIQUE(user_id, board_type, board_id)
);

CREATE INDEX idx_board_archives_user_type ON board_archives(user_id, board_type);