added spec for scroll behavior

packages/spright-components/src/chat/specs/scrolling-behavior.md

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+# Chat Component - Scrolling Behavior Specification
+
+## Overview
+This document defines the scrolling behavior for the chat component specifically system-initiated scrolling and how user-initiated scrolling impacts it.
+
+### Background
+- The Nigel chat needs defined scrolling behavior to balance automatic updates with user control
+
+### Types of Scrolling in AI Chat
+
+**User-initiated scrolling:**
+User initiated scrolling is done by the user to view previous chats in the message area. User scrolling can be initiated with the mouse, keyboard, or clicking on the scrollbar.
+-**Manual interruption:** A specific type of user scrolling that takes place when the user scrolls up while AI is generating response to stop auto-scroll.
+
+**System-initiated scrolling:**
+- **Post send auto-scroll:** Automatic scrolling to the users next message when the user sends a message
+- **AI response auto-scroll:** Scrolling as AI generates and streams response content
+
+## Auto-scrolling behavior
+
+**Post send auto-scroll**
+Post send auto-scrolling should appear any time the user sends a new message (regardless of where they are in the chat history at the time)
+
+**AI response auto-scroll**
+AI response auto-scroll should occur only if the AI streams responses. Long responses should auto scroll because streaming should be happening at a human readable pace and therefore start removing the old (assumed read) content off screen. If we are not streaming the response and instead returning a block of text, we should not autoscroll because this would take unread content off the screen.
+
+System-initiated auto-scrolling should stop when a manual interruption occurs. 
+
+**Auto-scroll Re-engagement**
+Auto scroll is re-rengaged when a user does any action to return to the bottom of the chat
+
+**Scroll position memory:**
+- Scroll position should only be preserved for the open chat, we do not need to remember scroll position history when navigating the chat history
+
+## Mouse Interactions
+
+### Scrolling Behavior
+- **Mouse wheel scrolling:** Standard scrolling behavior, disables auto-scroll when user scrolls up
+- **Scrollbar dragging:** Precise scroll control, temporarily disables auto-scroll
+
+## Non-Mouse Interactions
+
+### Keyboard Navigation
+- **Page Up/Down in message area:** Navigate through message history, disables auto-scroll
+- **Tab navigation:** Focus management doesn't affect scroll position for on screen elements but if we begin to tab upwards in the chat to nonvisible content we should scroll to it
+
+### Accessibility Considerations
+- **Screen readers:** Announce new messages without forcing scroll position changes
+- **Focus management:** Maintain logical tab order regardless of scroll position
+
+## Open Issues
+None