Add unit tests for weather endpoint error handling

[nivedithabinu]

In alertsystem.py, the /weather endpoint contains several error-handling branches but currently lacks the required test coverage.

This includes:

1. Missing city/state/country input
2. Missing OPENWEATHER_API_KEY
3. Invalid location not found
4. Unexpected internal exceptions

Without automated tests, future changes may accidentally break these error-handling paths without being detected.

To resolve this issue, we can cover these pytest test cases:

1. Missing required fields that return HTTP 400
2. Missing API key that return HTTP 500
3. Invalid location that return HTTP 404
4. Internal server exceptions that return HTTP 500

This will further improve the backend automation on this project.

I'd like to work on this issue if approved.

[nivedithabinu]

Hi, I'd like to work on this issue under SSoC '26, could you please assign this issue to me?
Thank you.

[Vikrant0207]

@nivedithabinu assigned

[nivedithabinu]

I pulled a PR request that resolves this issue, can you please look into it?