Fix continue watching advancing to the next episode before finishing the current one

[mehdigm4life]

Issue

When exiting the internal player during the last minutes of an episode — before it actually finished — the Continue Watching row would already show the next episode from the start, even though the current episode was never completed.

The reason: resume progress was saved on a milestone, and setViewPosAndResume immediately switched the "continue watching" entry to the next episode once progress reached 90% of the current one.

Fix

The next episode only becomes the resume target once the current episode has actually finished playing:

• DataStoreHelper.setViewPosAndResume now takes a completed flag. Unless the video reached its end, the resume entry stays on the current episode (at the position where you left).
• The completion is recorded where the video truly ends:
  • in GeneratorPlayer.nextEpisode() before advancing to the next episode, and
  • via a new onVideoEnded() callback for when autoplay is disabled and the player stays on the end screen.
• Added PlayerView.onVideoEnded() so host fragments are notified when playback reaches the end.

Behavior after the fix

• Leaving an episode at, e.g., 93% → Continue Watching keeps the same episode at 93%.
• Only finishing/watching to the end moves Continue Watching to the next episode (or removes the show from the row if it was the last episode).

Verified by compiling with :app:compileStableDebugKotlin. No settings or UI changes.

[mehdigm4life]

Closed to reopen a fresh PR with the same changes. (build check need approval)