test(impact): reject non-uuid ngoId

[Bhargi777]

Closes #152

Summary

• Assert that malformed GET /impact/:ngoId input returns HTTP 400.

Validation

• git diff --check and targeted Prettier check passed.
• npm run lint passed.
• npm run typecheck is blocked by the existing origin/main missing @fastify/compress dependency.
• Integration test execution requires PostgreSQL; this environment has no Docker/Postgres service.