Fix viewer timer and lifecycle review findings

- tick() refreshes lastTick on every tick, so a failed video no longer
  advances at once with its whole playback time.
- Photo timer counts only once the photo is shown (or failed), so a slow
  load cannot advance before display.
- Slides started while the activity is stopped stay paused and stopped;
  onStart re-prepares them.
- toggleLike error UI guard no longer indexes a replaced playlist.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

0 files changed, 0 insertions, 0 deletions