fix: accept external file drops in dragMoveEvent

[b10102016]

Summary

• dragMoveEvent was calling event->ignore() whenever the cursor was not hovering over an existing playlist item, which silently rejected all OS-level file drops landing on empty playlist space.
• The flow was: dragEnterEvent correctly accepted URL drops, but dragMoveEvent immediately cancelled them before dropEvent was ever reached.
• Fix: check hasUrls() at the top of dragMoveEvent and call �cceptProposedAction() for external file drops, bypassing the drop-target logic which only applies to internal item reordering.

Test plan

• Drag a video/YUV file from Windows Explorer onto the playlist area — file should load
• Drag a file onto an empty playlist — file should load
• Drag items within the playlist to reorder — internal reordering still works

🤖 Generated with Claude Code

[b10102016]

Closing in favor of #659 which addresses the same drag-and-drop issue.