Add a standalone architecture page at the start of the Disaggregated Storage section explaining leader/follower responsibilities, application versus WiredTiger ownership of role changes, and their effects across checkpoints, shared metadata/history store, handles, eviction, and background work. Include short step-up/step-down summaries and an animated leader/follower illustration with playback controls and a static fallback. Detailed async step-down behavior and concurrency analysis are follow-ups.