Timeline Sync

Mastodon provides a [markers API](https://docs.joinmastodon.org/methods/markers/) that could allow for timeline sync in Phanpy and other apps. It'd be great if timeline sync could be added, to sync between devices! I currently use this feature on Ivory (which uses its own API for this, not Mastodon's) and being able to jump between phone/desktop is really neat.

[Not even the official web version of Mastodon uses this API yet](https://github.com/mastodon/mastodon/issues/19036), so I am not sure how reliable it is, but could be worth giving it a shot?

Start by reading Mastodon's markers API documentation linked in the issue and inspect Phanpy's timeline and account-sync entry points. Determine how timeline positions should be stored and exchanged between devices, then verify that switching devices restores the expected position without disrupting timeline use.

Written by the indexing model from the issue text.