[Feature Request] Task support (CalDAV?)

[RokeJulianLockhart]

I currently use https://app.raindrop.io for my wishlist. However, it's not ideal, I have no way of marking a task as complete or incomplete except with tags. This doesn't provide an adequate visual cue or organization, since I can't set permanent per-(folder/tag) sorting and filtering.

https://github.com/wishlephant/wishlephant-website/issues/1 is the ideal solution.

Relevant:

0. [ ] https://gitlab.com/gitlab-org/gitlab/-/issues/14390
1. [ ] https://github.com/kaleidos-ventures/taiga-back/issues/128#issue-1688815129
2. [ ] https://github.com/wishlephant/wishlephant-website/issues/1#issue-1782844817
3. [ ] https://github.com/bookwyrm-social/bookwyrm/issues/2952#issue-1847099016
4. [ ] https://github.com/recloudstream/cloudstream/issues/550#issue-1847127445
5. [ ] https://github.com/LagradOst/QuickNovel/issues/184#issue-1847122964
6. [ ] https://github.com/ValveSoftware/steam-for-linux/issues/10019#issue-1868495803