Fix AI chat re-renders and refactored code (#18585)

This PR: 

- Breaks useAgentChatData into focused effect components (streaming,
fetch,
init, auto-scroll, diff sync)
- Splits message list into non-last (stable) + last (streaming/error) to
prevent full re-renders on each stream chunk
- Adds scroll-to-bottom button and MutationObserver-based auto-scroll on
thread switch
- Lifts loading state from context to atoms
- Adds areEqual to selector
factories

We could improve further but this sets up a robust architecture for
further refactoring.

## Messages flow

The flow of messages loading and streaming is now more solid. 

Everything goes out from `AgentChatAiSdkStreamEffect`, whether loaded
from the DB or streaming directly, and every consumers is using only one
atom `agentChatMessagesComponentFamilyState`

## Data sync effect with callbacks new hook 

See
`packages/twenty-front/src/modules/apollo/hooks/useQueryWithCallbacks.ts`
which allows to fix Apollo v4 migration leftovers and is an
implementation of the pattern we talked about with @charlesBochet

We could refine this pattern in another PR.

# Before



https://github.com/user-attachments/assets/84e7a96f-6790-405d-8a73-2dacbf783be5


# After



https://github.com/user-attachments/assets/4c692e3a-2413-4513-abcc-44d0da311203

Co-authored-by: Charles Bochet <charles@twenty.com>

packages/twenty-front/src/modules/side-panel/components/SidePanelTopBarRightCornerIcon.tsx

@@ -10,7 +10,7 @@ import { IconButton } from 'twenty-ui/input';
 import { useIsMobile } from 'twenty-ui/utilities';
 import { FeatureFlagKey } from '~/generated-metadata/graphql';
 
-import { useCreateNewAIChatThread } from '@/ai/hooks/useCreateNewAIChatThread';
+import { useSwitchToNewAIChat } from '@/ai/hooks/useSwitchToNewAIChat';
 import { themeCssVariables } from 'twenty-ui/theme-constants';
 
 const StyledIconButtonContainer = styled.div`
@@ -22,7 +22,7 @@ export const SidePanelTopBarRightCornerIcon = () => {
   const isAiEnabled = useIsFeatureEnabled(FeatureFlagKey.IS_AI_ENABLED);
   const sidePanelPage = useAtomStateValue(sidePanelPageState);
   const { openAskAIPage } = useOpenAskAIPageInSidePanel();
-  const { switchToNewChat } = useCreateNewAIChatThread();
+  const { switchToNewChat } = useSwitchToNewAIChat();
 
   if (isMobile || !isAiEnabled) {
     return null;