Revert: Agent chat umbrella hook refactoring due to streaming issue on thread switch (#15621)

## Summary

Reverts commits afc518a, ae22e64, and 800b5b5 that refactored
`useAgentChat` to address umbrella hook pattern feedback.

## Issues Introduced by Refactoring

The refactoring broke several critical functionalities:

1. **Streaming fails on thread switch** - Messages don't stream properly
when switching between threads
2. **Messages lost on tab close** - When the Ask AI tab is closed, the
request is lost instead of continuing in the background
3. **Blank chat requiring force-reload** - Chats often appear blank and
require switching to another chat to force a reload (closes
[#1771](https://github.com/twentyhq/core-team-issues/issues/1771))

## Root Cause

After extensive debugging, it appears **multiple instances of `useChat`
don't work well together**. The refactored architecture inadvertently
created scenarios where multiple `useChat` instances interfere with each
other.

## Resolution

Reverting to restore functionality. The umbrella hook pattern
optimization needs a different architectural approach that doesn't rely
on multiple `useChat` instances.

## Follow-up

While the umbrella hook feedback is valid, we need to rethink the
implementation strategy:
- Find an alternative to multiple `useChat` instances
- Possibly consolidate chat state management differently

packages/twenty-front/src/modules/ai/components/internal/SendMessageButton.tsx

@@ -1,13 +1,8 @@
 import { AI_CHAT_INPUT_ID } from '@/ai/constants/AiChatInputId';
-import { useAgentChat } from '@/ai/hooks/useAgentChat';
 import { useAgentChatContextOrThrow } from '@/ai/hooks/useAgentChatContextOrThrow';
-import { useAgentChatRequestBody } from '@/ai/hooks/useAgentChatRequestBody';
-import { agentChatUploadedFilesState } from '@/ai/states/agentChatUploadedFilesState';
 import { type ObjectRecord } from '@/object-record/types/ObjectRecord';
 import { useHotkeysOnFocusedElement } from '@/ui/utilities/hotkey/hooks/useHotkeysOnFocusedElement';
-import { useChat } from '@ai-sdk/react';
 import { t } from '@lingui/core/macro';
-import { useRecoilState } from 'recoil';
 import { Key } from 'ts-key-enum';
 import { Button } from 'twenty-ui/input';
 
@@ -16,40 +11,14 @@ export const SendMessageButton = ({
 }: {
   records?: ObjectRecord[];
 }) => {
-  const { input, isLoading, handleInputChange } = useAgentChat();
-  const { chat } = useAgentChatContextOrThrow();
-  const { buildRequestBody } = useAgentChatRequestBody();
-  const { sendMessage } = useChat({ chat });
-
-  const [agentChatUploadedFiles, setAgentChatUploadedFiles] = useRecoilState(
-    agentChatUploadedFilesState,
-  );
-
-  const handleSendMessage = () => {
-    if (input.trim() === '' || isLoading) {
-      return;
-    }
-
-    sendMessage(
-      {
-        text: input,
-        files: agentChatUploadedFiles,
-      },
-      {
-        body: buildRequestBody(records),
-      },
-    );
-
-    handleInputChange('');
-    setAgentChatUploadedFiles([]);
-  };
+  const { handleSendMessage, isLoading, input } = useAgentChatContextOrThrow();
 
   useHotkeysOnFocusedElement({
     keys: [Key.Enter],
     callback: (event: KeyboardEvent) => {
       if (!event.ctrlKey && !event.metaKey) {
         event.preventDefault();
-        handleSendMessage();
+        handleSendMessage(records);
       }
     },
     focusId: AI_CHAT_INPUT_ID,
@@ -62,7 +31,7 @@ export const SendMessageButton = ({
   return (
     <Button
       hotkeys={input && !isLoading ? ['⏎'] : undefined}
-      onClick={handleSendMessage}
+      onClick={() => handleSendMessage(records)}
       disabled={!input || isLoading}
       variant="primary"
       accent="blue"