Update ChatBackend .http file with all project APIs and token handling

Include all endpoints from the project (GET, POST, PUT, DELETE) for all modules.
Use the base URL variable.
Add token handling for APIs requiring authentication.
Use `Authorization: Bearer {{AuthToken}}` in headers
- Optionally, include a login request to fetch the token.
Include sample request bodies for POST/PUT endpoints
Include proper headers like `Accept: application/json` and `Content-Type: application/json`
Maintain clear section headings for each API for readability.