refactor: shift grade summary calculation to backend and display "hidden grades" label in the grade table (#1797)

Refactors the grade summary logic to delegate all calculation responsibilities to the backend.
Previously, the frontend was performing grade summary computations using data fetched from the API. Now, the API itself provides the fully computed grade summary, simplifying the frontend and ensuring consistent results across clients.

Additionally, a "Hidden Grades" label has been added in the grade summary table to clearly indicate sections where grades are not visible to learners.

Finally, for visibility settings that depend on the due date, this PR adds a banner on the Progress page indicating that grades are not yet released, along with the relevant due date information.