fix: remove dead code, fix naming inconsistency, document migration

- Remove unused AGENT_CHAT_RETRY_EVENT_NAME constant (dead code)
- Rename agentStreamingService to agentChatStreamingService for consistency
- Add comment explaining why migration down() deletes queued messages

https://claude.ai/code/session_01NGv3c62sYGMww7iuVsWzcJ

packages/twenty-front/src/modules/ai/constants/AgentChatRetryEventName.ts

@@ -1 +0,0 @@
-export const AGENT_CHAT_RETRY_EVENT_NAME = 'agent-chat-retry' as const;

packages/twenty-server/src/database/typeorm/core/migrations/common/1774776000000-add-status-to-agent-message.ts

@@ -25,6 +25,8 @@ export class AddStatusToAgentMessage1774776000000
     await queryRunner.query(
       `ALTER TABLE "core"."agentMessage" DROP COLUMN "processedAt"`,
     );
+    // Queued messages have turnId=NULL. They must be deleted before
+    // restoring the NOT NULL constraint on turnId.
     await queryRunner.query(
       `DELETE FROM "core"."agentMessage" WHERE "turnId" IS NULL`,
     );

packages/twenty-server/src/engine/metadata-modules/ai/ai-chat/controllers/agent-chat.controller.ts

@@ -52,7 +52,7 @@ import { AiModelRegistryService } from 'src/engine/metadata-modules/ai/ai-models
 )
 export class AgentChatController {
   constructor(
-    private readonly agentStreamingService: AgentChatStreamingService,
+    private readonly agentChatStreamingService: AgentChatStreamingService,
     private readonly agentChatService: AgentChatService,
     private readonly eventPublisherService: AgentChatEventPublisherService,
     private readonly billingService: BillingService,
@@ -132,7 +132,7 @@ export class AgentChatController {
       return { messageId: message.id, queued: true };
     }
 
-    const result = await this.agentStreamingService.streamAgentChat({
+    const result = await this.agentChatStreamingService.streamAgentChat({
       threadId,
       browsingContext: body.browsingContext ?? null,
       modelId: body.modelId,