openai/gpt-chat-latest → B (5:1)

Side B fixes a real reducer correctness bug by moving the zero-ratio early return before `ensure_item` and `voted_pairs.insert`, preventing ghost items and incorrectly recorded voted pairs, and updates the test to verify that no state is registered. Side A primarily removes the obsolete monolithic `forum.rs` and switches to the split `forum/` module layout, which improves project structure but largely preserves existing behavior rather than fixing functionality.