feat: add resumable stream support for agent chat (#19107)

## Overview
Add resumable stream support for agent chat to allow clients to
reconnect and resume streaming responses if the connection is
interrupted (e.g., during page refresh).

## Changes

### Backend (Twenty Server)
- Add `activeStreamId` column to `AgentChatThreadEntity` to track
ongoing streams
- Create `AgentChatResumableStreamService` to manage Redis-backed
resumable streams using the `resumable-stream` library with ioredis
- Extend `AgentChatController` with:
  - `GET /:threadId/stream` endpoint to resume an existing stream
  - `DELETE /:threadId/stream` endpoint to stop an active stream
- Update `AgentChatStreamingService` to store streams in Redis and track
active stream IDs
- Add `resumable-stream@^2.2.12` dependency to package.json

### Frontend (Twenty Front)
- Update `useAgentChat` hook to:
- Use a persistent transport with `prepareReconnectToStreamRequest` for
resumable streams
  - Export `resumeStream` function from useChat
  - Add `handleStop` callback to clear active stream on DELETE endpoint
- Use thread ID as stable message ID instead of including message count
- Add stream resumption logic in `AgentChatAiSdkStreamEffect` component
to automatically call `resumeStream()` when switching threads

## Database Migration
New migration `1774003611071-add-active-stream-id-to-agent-chat-thread`
adds the `activeStreamId` column to store the current resumable stream
identifier.

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

packages/twenty-server/src/database/typeorm/core/migrations/common/1774003611071-add-active-stream-id-to-agent-chat-thread.ts

@@ -0,0 +1,19 @@
+import { MigrationInterface, QueryRunner } from 'typeorm';
+
+export class AddActiveStreamIdToAgentChatThread1774003611071
+  implements MigrationInterface
+{
+  name = 'AddActiveStreamIdToAgentChatThread1774003611071';
+
+  public async up(queryRunner: QueryRunner): Promise<void> {
+    await queryRunner.query(
+      `ALTER TABLE "core"."agentChatThread" ADD "activeStreamId" character varying`,
+    );
+  }
+
+  public async down(queryRunner: QueryRunner): Promise<void> {
+    await queryRunner.query(
+      `ALTER TABLE "core"."agentChatThread" DROP COLUMN "activeStreamId"`,
+    );
+  }
+}