Improve alert presentation and prevent blank toast messages

[iHateErrorsSoMuch]

This pull request focuses on improving the alert presentation and notification feedback within the Android application. During testing, it was observed that some API responses resulted in blank or unclear toast messages, which negatively impacted the user experience.

Problem Identified: -

1. Certain API error responses returned an empty or null apiError field.
2. This caused the application to display blank toast messages, providing no useful feedback to the user.
3. Success responses relied on response.message(), which could be unclear or inconsistent

Changes Implemented: -

1. Added fallback error handling to ensure that users always see a meaningful message when an error occurs
2. Replaced unreliable API response messages with clear and consistent user-friendly messages
3. Added a success message ("Patient added successfully") to improve feedback after successful operations
4. Improved overall frontend behaviour for alert handling

Additionally, this update ensures that users receive clear and consistent feedback during both successful and failed operations. By eliminating blank toast messages, the overall user experience is improved, making the application more reliable and easier to use.