idea: self-hosted calendar server

[MathiasDevelopes]

It would be a great idea to create a calendar server which would serve updated calendar from VIS InSchool.

Auth also needs to be solved, and this should probably be implemented after #28

[MathiasDevelopes]

It should be straight forward when we can reuse most of the code, but the biggest challenges lay in authentication.

I have attached a poc file written by ai which i have successfully used to obtain an authenticated visma session.

This could be used as a reference for implementing this in TypeScript.

inschool_auth.py