Wait for a seek from the end to take effect before playing

[danielchalmers]

Pressing play on a clip that has finished often left the video frozen on its first frame while the transport showed "playing". Seeking back from the end and then pressing play froze almost every time. This predates v1.0.0.

Cause

From FlyleafLib's own source (Player.Playback.cs, v3.11.5):

• Play() returns without doing anything while status == Status.Ended (line 37).
• A seek issued from Ended only flips the status back to Paused later, from the background task that performs the seek (lines 256–260).

PlayAsync handles a finished clip by seeking to the start and playing back to back. So Play() usually lands before that task has run, gets dropped, and the controller reports playback that never started.

Fix

FlyleafCameraPlayer.SeekAsync notes whether the player was Ended when the seek was issued, and if so waits for the status to leave Ended before returning. Player.Status reads the live field rather than a dispatcher-updated copy, so the flip is visible the moment it happens and the wait is normally a few milliseconds. A 1s cap keeps a seek that never runs from stalling the caller. Seeks from any other state return immediately, as before.

Measured

Real stack, FlyleafLib 3.11.5, 30 iterations each. Every check requires the player's own clock to advance, because a clip frozen at zero also reports IsPlaying and a small Position.

scenario	before	after
play after the clip finishes	16/30	30/30
seek back from the end, then play	0/30	30/30
seek just before the end, play immediately	15/30	30/30
play from just before the end	30/30	30/30

With FlyleafLib 3.10.4, the library v1.0.0 shipped, the first two froze 8/20 and 16/20. This isn't a regression from the recent upgrades.

The integration harness passes 140/140 with the fix: install, playback, six-camera sync, unreadable chunks, file handles, export and color. Its replay check now requires real movement; the old version passed on a clip frozen at zero, which is how this went unnoticed.

This is Flyleaf behavior that the unit-suite fakes don't model, so there's no unit test. 374 tests green, dotnet format --verify-no-changes clean.

How to verify by hand

Open any clip, let it play to the end (or scrub to the end), then press Space. The video should play from the start. Before this change it often stayed on the first frame while the play button showed pause.