Fix auto-scroll to only trigger during streaming (#1593)

Previously, the chat auto-scrolled whenever messages changed, even when
not streaming. This caused unwanted scrolling when switching chats or
loading messages from the database.

Now auto-scroll only triggers when:
- Messages are actively streaming (isStreaming is true)
- User hasn't manually scrolled away
- User is near the bottom of the chat

Changes:
- Added isStreamingByIdAtom to track streaming state
- Modified auto-scroll useEffect to check isStreaming before scrolling
- Preserved streamCount effect for initial scroll on stream start

🤖 Generated with [Claude Code](https://claude.com/claude-code)
    
<!-- This is an auto-generated description by cubic. -->
---

## Summary by cubic
Fixes chat auto-scroll so it only runs during active streaming,
preventing jumps when switching chats or loading message history.

- **Bug Fixes**
- Added isStreamingByIdAtom and gated the auto-scroll effect by per-chat
streaming state (updated effect deps).
  - Preserved the initial scroll on stream start via streamCount.

<!-- End of auto-generated description by cubic. -->

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Limits chat auto-scroll to when a conversation is actively streaming
and the user is near the bottom.
> 
> - **Frontend**
> - **Chat auto-scroll behavior**: Only auto-scrolls during active
streaming.
> - Adds `isStreamingByIdAtom` and reads per-chat `isStreaming` state.
> - Updates auto-scroll `useEffect` to require `isStreaming` and adds it
to dependencies.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
6580601cd974c2c01ddffdef78ed0ddbb2b2fa8d. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Co-authored-by: Claude <noreply@anthropic.com>

src/components/ChatPanel.tsx

@@ -3,6 +3,7 @@ import { useAtomValue, useSetAtom } from "jotai";
 import {
   chatMessagesByIdAtom,
   chatStreamCountByIdAtom,
+  isStreamingByIdAtom,
 } from "../atoms/chatAtoms";
 import { IpcClient } from "@/ipc/ipc_client";
 
@@ -30,6 +31,7 @@ export function ChatPanel({
   const [isVersionPaneOpen, setIsVersionPaneOpen] = useState(false);
   const [error, setError] = useState<string | null>(null);
   const streamCountById = useAtomValue(chatStreamCountByIdAtom);
+  const isStreamingById = useAtomValue(isStreamingByIdAtom);
   // Reference to store the processed prompt so we don't submit it twice
 
   const messagesEndRef = useRef<HTMLDivElement | null>(null);
@@ -131,10 +133,13 @@ export function ChatPanel({
   }, [fetchChatMessages]);
 
   const messages = chatId ? (messagesById.get(chatId) ?? []) : [];
-  // Auto-scroll effect when messages change
+  const isStreaming = chatId ? (isStreamingById.get(chatId) ?? false) : false;
+
+  // Auto-scroll effect when messages change during streaming
   useEffect(() => {
     if (
       !isUserScrolling &&
+      isStreaming &&
       messagesContainerRef.current &&
       messages.length > 0
     ) {
@@ -145,7 +150,7 @@ export function ChatPanel({
         });
       }
     }
-  }, [messages, isUserScrolling]);
+  }, [messages, isUserScrolling, isStreaming]);
 
   return (
     <div className="flex flex-col h-full">