Wire the eight NowPlayingState transport callbacks (toggle_play, next,
previous, seek, set_volume, toggle_mute, toggle_shuffle, cycle_repeat) with the
"try remote -> fall back to local" pattern: each spawns a task that calls the
matching *_if_remote method; Ok(true) short-circuits (forwarded to the active
peer), Ok(false)/no-service falls through to the existing playback::* local
call unchanged. Includes the seek fraction->ms (via local duration), volume
0..1->0..100, and mute-negation conversions.
Adds playback::is_muted() to read the authoritative local mute flag for the
mute handoff. No regression to renderer/local playback: the remote gate is
is_peer_renderer_active, so every non-controller branch returns Ok(false).
cc
vicrodh
126e9da1db