Replay and GameViewer Integration Refactoring

[smly]

Currently, Replay (riichienv-core/src/replay/) and GameViewer (riichienv-ui/, src/riichienv/visualizer/) have independent implementations. Consolidate the shared game state management layer and reduce code duplication.

• Clarify responsibilities between riichienv-ui/src/game_state.ts and Rust-side Replay logic
• Design a common event processing interface
• Extract shared foundation for LiveViewer and ReplayViewer
• Unify game state management via WASM (reduce TypeScript-side state logic)
• Integrate Replay/Live modes in the Python Viewer (viewer.py)