Ensure Frontend Handles Standardized Backend Responses

### Description:

The frontend currently lacks consistency in handling API responses, leading to incorrect or missing user feedback. We need to update all frontend logic to align with the backend's standardized response structure (such as `EmailValidationResponse` and `EmailResponse`).

#### Goals:

* Update frontend API handling to properly read and use:

* `status`
* `message`
* `data` (if present)
* Display backend-provided messages to users using `response.message`
* Make decisions based on the actual `status` value (`SUCCESS`, `FAILED`, etc.)
* Remove hardcoded or outdated logic related to API responses

#### Example:

```js
// Instead of:
if (res.ok) { show("Success") }

// Use:
if (res.status === "SUCCESS") {
show(res.message)
}
```