Add pre-emptive checks to prevent disallowed user actions #103

[Sanika123-art]

Summary

This pull request adds pre-emptive validation checks to prevent disallowed user actions when creating a round.

Previously, certain invalid inputs (such as missing jurors, invalid quorum values, or invalid Wikimedia Commons categories) could cause the backend to return a 500 Internal Server Error. This PR adds validation logic so that these cases are handled gracefully and return appropriate error messages instead of crashing the server.

Changes Made

*Added validation for missing jurors before creating a round.

• Added validation for invalid quorum values (quorum must be greater than 0).
• Added validation for invalid or empty Wikimedia Commons categories during image import.
• Added proper error handling to return HTTP 400 responses instead of causing 500 server errors.

Expected Behavior

• If a user attempts to create a round without jurors, the system returns a validation error.
• If quorum is set to an invalid value, the request is rejected.
• If an invalid category is provided for image import, the backend returns a clear error message instead of crashing.

Result

These checks prevent backend crashes and improve system stability by ensuring invalid user actions are caught before processing.