Increase Unit Test Coverage for Backend Handlers

[armaan-71]

Context

We currently rely on manual verification. We need robust unit tests to ensure stability as the codebase grows.

Goals

• Add Jest unit tests for createRun and processRun handlers.
• Mock AWS SDK calls using aws-sdk-client-mock.

Implementation Details

• Configure Jest in backend/ directory.
• Write tests for:
  • Success scenarios (correct DynamoDB calls).
  • Error handling (e.g., dynamo write failure).
  • Input validation.