feat(whatsapp): implement native typing indicators via Cloud API

[JuanBifrost]

Summary

Implements native WhatsApp typing indicators via the WhatsApp Business Cloud API according to Meta's official documentation:
https://developers.facebook.com/documentation/business-messaging/whatsapp/typing-indicators

Context & Problem

Previously, the WhatsApp conversation handler attempted to call markAsRead with a hardcoded "lastMessageId" dummy string and did not implement typing indicator payloads. Additionally, flow steps executing typing did not pause execution to allow the typing indicator to remain visible before sending the subsequent message.

Changes

1. SDK (packages/sdk):

   • Extended ConversationHandlers["sendTyping"] input type with optional messageId?: string.

2. Worker Config (packages/worker-config):

   • Added optional messageId?: string to ChatJobSendTyping["data"].

3. WhatsApp Integration (integrations/whatsapp):

   • Implemented native sendTyping using whatsappClient.$$apiFetch$$ with the official Meta endpoint POST /<API_VERSION>/<PHONE_NUMBER_ID>/messages and payload:

     {
       "messaging_product": "whatsapp",
       "status": "read",
       "message_id": "<INCOMING_MESSAGE_ID>",
       "typing_indicator": {
         "type": "text"
       }
     }

   • Gracefully handles missing messageId and API/network errors without throwing unhandled exceptions.
   • Cleared broken "lastMessageId" dummy call in agentMarkAsRead.

4. Worker Step Execution (apps/worker):

   • In stepSendTyping, dynamically resolves the latest incoming message ID (sourceId) for the conversation via messageService.findLatestIncomingMessage (following the service -> repository -> DB pattern).
   • Pauses execution via setTimeout for the configured duration (props.step.seconds, clamped between 1s and 60s) so the typing indicator remains visible on the user's phone before subsequent flow messages are dispatched.
   • Forwarded messageId in sendTypingToChannel (with fallback lookup for WhatsApp) and in processAutomatedResponse (triggerMessage?.sourceId).

5. Unit Tests:

   • Added integrations/whatsapp/__tests__/conversation-typing.test.ts to test typing payloads, missing ID handling, and error resiliency.
   • Added apps/worker/__tests__/step-typing-handler.test.ts to test step delay, message lookup, and channel dispatch.

Verification

• Tested locally and in production deployment with WhatsApp Cloud API: typing indicator (... escribiendo) renders on device during configured step seconds before response message arrives.
• Unit tests added and passing for both integration handler and worker step handler.