feat(docs): implement comprehensive Chat and ChatId schemas for Swagger

[kaua-alves-queiros]

📚 API Documentation Enhancement – Chat Schemas

This PR improves the API documentation by introducing explicit schemas for chat-related responses. As a result, the Swagger UI now accurately represents the data structures used in WhatsApp chat management.

---

✅ Changes

• Schema Definitions
  Added the following schemas to swagger.js and swagger.json:

  • ChatId
  • Chat
  • GetChatsResponse

• Controller Integration
  Updated getChats and getChatsWithSearch in clientController.js to leverage the new $ref schema definitions.

• Documentation Clarity
  Refined endpoint descriptions related to chat retrieval, clearly specifying session-based behavior.

---

🚀 Impact

• Provides clear and consistent expectations for the Chat object structure, including:
  • unreadCount
  • isGroup
  • Serialized ChatId

---

⚠️ Important Note on Chat Schema

[!IMPORTANT]
The current Chat schema represents a base version.
The lastMessage property and its associated nested models will be added in a future PR, once the required message schemas are finalized.