v1.4.1

Fix mirrored panes freezing open when a window is closed

When a window closed but its app kept running, macOS kept returning the
window's last frame from screencapture instead of erroring, so the picture
looked merely static (0 fps) and the close-detection — which only ran on a
capture failure — never fired. The window left the picker immediately but its
pane stayed frozen on the last frame indefinitely.

- exists() now checks the same on-screen list the picker uses
  (kCGWindowListOptionOnScreenOnly) instead of kCGWindowListOptionAll; the
  "All" list retained a closed window's still-capturable backing store, which
  is exactly what kept the pane alive.
- streamWindow proactively re-verifies a static window is still on-screen
  (every winLiveCheck) rather than waiting for a capture failure that may never
  come, and drops the pane when it's gone.

Occluded windows stay on-screen so they're unaffected; minimizing or moving a
mirrored window to another Space now closes its pane too, matching the picker.

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