fix(details): show the watchlist bookmark at once instead of after Trakt and cloud sync

[ReichiMD]

Summary

Tapping the watchlist bookmark on the details page takes 3-5 seconds to tick or untick when Trakt and an ARVIO account are connected (reported by a user on Discord, reproduced on a phone: 4-5 s in both directions). toggleWatchlist() only updated isInWatchlist after the Trakt/SIMKL write, the local save and cloudSyncRepository.pushToCloud(), which waits for the cloud-sync lock, downloads the server snapshot and then uploads the account state.

Changes

• Details page (DetailsViewModel.toggleWatchlist): the bookmark and the toast flip right away; the Trakt/SIMKL write and the local save follow, and the cloud push runs only after a successful save. If the write fails, the bookmark goes back and the existing error toast shows (before, it silently stayed off).
• Double tap: writes run one at a time under a mutex and save whatever the bookmark shows at that moment, so they cannot finish out of order. Two taps that cancel each other out write nothing.
• Initial load: the page load's watchlist read no longer overwrites a tap made while it was still running.
• Home long-press menu (HomeViewModel.toggleWatchlist): the confirmation toast now shows before the cloud push instead of after it. The flow is otherwise unchanged.

The library's remove already showed its result before pushToCloud(); this brings the details page in line with it.

Testing

• New DetailsWatchlistToggleTest (5 cases): hanging cloud push, Trakt failure, second tap while the first save is running, second tap after a failed first save, tap during the initial load. Four of the five fail on current main.
• Full testSideloadDebugUnitTest: 1728 tests green.
• Phone (sideload debug build, ARVIO account + Trakt connected): the bookmark ticks and unticks instantly for a movie and a series (before: 4-5 s in both directions). A quick double tap ends in the state shown, also after leaving and reopening the page, and the title appears in the Trakt watchlist.

created by Claude (Anthropic) on behalf of @ReichiMD