refactor(webhook): deduplicate webhook body types and message extraction

[jerrzxy]

Overview

This PR consolidates the duplicated WhatsApp webhook body modeling into a single shared module. Previously, bot.controller.ts, webhook-signature.middleware.ts, and command-rate-limit.middleware.ts each declared their own body types and independently traversed entry[0].changes[0].value.messages[0]. This change introduces one shared definition of the wire format plus a single readFirstMessage accessor, and rewires all three call sites to consume it — while preserving the controller's stricter validation and the middleware's looser reads via options.

Related Issue

Changes

🧩 Shared Webhook Body Module

• [MODIFY] src/services/whatsapp.service.ts
  • Now declares the canonical webhook body types (WhatsAppContact, WhatsAppTextMessage, WhatsAppMessage, WhatsAppStatus, WhatsAppChangeValue, WhatsAppChange, WhatsAppEntry, WhatsAppWebhookBody).
  • Adds a single readFirstMessage(body) accessor that performs the one traversal of entry → changes → value → messages[0].
  • Supports option flags so callers can request stricter validation (non-empty strings, required message id) without a second traversal.

🔌 Call Site Refactors

• [MODIFY] src/controllers/bot.controller.ts

  • Removes its local body type declarations and imports them from the shared module.
  • extractTextMessage now delegates to readFirstMessage with strict options, so it still rejects a message without an id or an empty body.

• [MODIFY] src/middleware/webhook-signature.middleware.ts

  • Removes its local WhatsAppMessage, WhatsAppStatus, and WhatsAppWebhookBody declarations.
  • extractReplayInfo consumes the shared accessor with loose options.

• [MODIFY] src/middleware/command-rate-limit.middleware.ts

  • extractMessageDetails consumes the shared accessor instead of traversing the body itself.

Verification Results

npm test
✅ passes locally

Acceptance Criteria	Status
One module declares the webhook body types and the traversal	✅ Types and readFirstMessage live in whatsapp.service.ts
All three call sites import it and define no body shape of their own	✅ Controller and both middlewares import shared types
The controller still rejects a message without an id or an empty body	✅ Strict options preserved in extractTextMessage
npm test passes locally	✅ Verified

Closes #115

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