Feature/mu ed (#260)

* Added Postman collection for testing `compareExpressions` API

* Switched Dockerfile to use `feature-muEd-3.8` base image

* Refactored Postman collection to support local and cloud modes, standardized variable handling.

* Switched to use on dev workflow for testing updated deployment API

* Enabled pre-submission feedback support in Postman collection for MuEd evaluation and preview requests.

* Updated staging deploy workflow to use `deploy-request` instead of `deploy-request-on-dev`.

* Added extensive case-matching tests and feedback handling for Chunk 11 in Postman collection

* Added tests for `responseLatex` and `responseSimplified` fields in Postman collection.

Author: m-messer