- Relocated TopicStickyHeader from chat history to global AppLayouts (Default and ScreenReader) for permanent viewport stickiness.
- Fixed duplication issues by removing complex history injection logic in MainContent.tsx.
- Restored natural rendering of topic updates in chat history to ensure consistent scrollback context.
- Added persistent styling (background and separator) to TopicStickyHeader for better visual hierarchy.
- Simplified MainContent.tsx logic by removing redundant overlay and virtualization hacks.
- Updated unit tests and snapshots to align with the new stable layout architecture.