Movie Editor: Play from end-of-timeline restarts from the beginning

If the playhead is at/past the end (or on no clip) when Play is pressed, reset it to 0 and
play from the top instead of doing nothing.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

movie_editor/frontend/player.js

@@ -181,6 +181,8 @@
   }
 
   function _play() {
+    // At (or past) the end of the timeline → loop the playhead back to the start.
+    if (_phSec >= (_totalSecCur || 0) - 0.05 || !_clipFrom(_phSec)) _phSec = 0;
     const clip = _clipFrom(_phSec);
     if (!clip) return;
     if (_phSec < clip.startSec) _phSec = clip.startSec;