fix: resolve multi-turn chat UI bugs for completed turns

[myeolinmalchi]

Summary

• Fix todosFromState leaking previous turn's todos into new turns by requiring todosFromMessages presence before using global state
• Remove incorrect isIntermediateNodeMessage filter for completed turns that hid final AI responses when message.name didn't match finalNodeNames
• Replace CompletedTurnTaskView accordion with inline StreamingTaskView so completed turns display identically to streaming view
• Discovered and backported from downstream fork bug fixes