Bug: /add endpoint returns 200 instead of 201 for new calculations

[ascerra]

Description

The /add endpoint returns HTTP 200 for successful addition operations. Per REST conventions, creating a new calculation result should return 201 Created.

Steps to reproduce

curl -X POST http://localhost:5000/add -H "Content-Type: application/json" -d '{"a": 2, "b": 3}'
# Returns 200 OK with {"result": 5}

Expected behavior

Should return 201 Created with the result body.

Actual behavior

Returns 200 OK.

[rh-rahulshetty]

/fs-code