Clean up of database.ts or « Conceding to the robot »

[AKArien]

on pr #133, someone less smart than me asked an llm to review my code.

While i may have been not very receptive to criticism, notably saying mais je t’emmerde robot, there were some valid points, notably adding JSDoc snippets and using a function for the repeated error handling.
I am also fairly certain one could find some other cleanups.