Migrate chat.postMessage endpoint to new API route format #39591
Description
Description
The endpoint chat.postMessage is still implemented using the deprecated API.v1.addRoute format.
Rocket.Chat is gradually migrating endpoints to the new declarative API format (API.v1.post, API.v1.get, etc.) which provides:
- Typed request validation
- Response schema validation
- Improved OpenAPI generation
- Better maintainability
This issue proposes migrating the endpoint to the new format.
Current Implementation
API.v1.addRoute('chat.postMessage', {...})