fix(timestamp): change column type timestamp to timestamptz

[sthelemann]

I noticed that some table columns have data type timestamp while others have data type timestamptz.
We should generally use data type timestamptz (or timestamp with time zone).

[dargmuesli]

You're right! Good catch 🙏
Would you like to try implementing this change as next step? Small code changes allow for focus on understanding the git flow, then we can transition to tasks that are on the more extensive feature side as next step ✨