Remove old price model left overs

_Originally: https://github.com/virge-io/pricelist-frontend/issues/250_

Lot's of places still use the hardcoded fields: Frontend + Backend

KindDetail endpoint will be covered in other ticket #270

A CLI script is needed to convert the last remaining prices: there are still some "PrijsCombi's" that use a hardcoded joint or canna price; only PrijsCombi's that were used were converted.

This is a left over of bug/problems when we deployed the new model; we did some last minute changes in the convert to not harm horeca prices: which led to some "unconverted PrijsCombi's".

So write a script that finds these: and remove the hardcoded field values en replace it with the correct json prices. Probably good to check if noc actual ShopToPrice relation exists for them on the canna card.

The issue names no files or tests; start by locating the remaining hardcoded price fields and the existing price-conversion logic in the frontend and backend. Identify unconverted PrijsCombi records, check whether an actual ShopToPrice relation exists on the canna card, and verify that the CLI replaces eligible hardcoded values with the correct JSON prices without changing the KindDetail endpoint scope.

Rédigé par le modèle d'indexation à partir du texte de l'issue.