This epic collects some technical debt that we want to clean up as part of (and ahead of) functional changes. The work done in these subtasks should not affect any user-facing features, it's only meant to simplify and prepare the relevant code for our heavier feature-implementation.

To discuss: we have already included a buffer for legacy-code refactoring in all of the sidebar feature tasks. The dev team has suggested (in yesterday's Retro) that this epic and its subtask tree are accounted for by feature task point estimates already, so should not be estimated separately. The idea behind making tasks at all is to organize this work coherently and to make space for parallel development by multiple people.