[MattiasBuelens]

Summary

TV DefaultUI focuses the SeekBar when the controls appear, so Left/Right seek right away. Until now, Center did nothing on the seek bar, so to pause you first had to move focus down to the play button. Google's "Playback controls on TV" guide says Center should toggle play/pause, so the TV SeekBar now does that for Center, Enter and NumPad Enter.

• New SeekBarState.togglePlayPause() in ui-common. It plays or pauses the player. While the user is scrubbing, it doesn't touch the player and instead flips whether playback resumes in onValueChangeFinished(), so it doesn't fight the pause that scrubbing does.

  fun togglePlayPause() {
      if (seekTime != null) wasPlayingBeforeSeek = !wasPlayingBeforeSeek
      else if (player.isPaused) player.play() else player.pause()
  }

• TV SeekBar(state) calls state.togglePlayPause() on a KeyDown with repeatCount == 0. Repeats from a held key are consumed but don't toggle again.
• The seek bar only consumes a KeyUp that follows its own KeyDown. While the controls are hidden, tvHiddenControlsKeys consumes the Center KeyDown: it shows the controls and toggles playback. The seek bar may get focus before the KeyUp arrives, and ignoring that KeyUp means playback isn't toggled a second time.

Tests:

• SeekBarStateTest covers toggling normally and during a scrub.
• SeekBarTest covers Center and Enter, holding Center, and a KeyUp without a KeyDown.
• DefaultUITest covers Center on the focused seek bar, and a full Center press while the controls are hidden, which toggles exactly once.

The TV guides and the changelog are updated.

Link to Devin session: https://dolby.devinenterprise.com/sessions/63210218adb6456ab0406d4eb65d28e9
Open in Devin Desktop: https://dolby.devinenterprise.com/desktop/session/63210218adb6456ab0406d4eb65d28e9?variant=devin
Requested by: @MattiasBuelens

[devin-ai-integration]

I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".

• Disable automatic comment, CI, and merge conflict monitoring