NX Sentry 0.3.0

Two things: the alarm can now choose where it plays, and the selector zooms.

Play the alarm on — a device picker in the Alarm panel. If your desktop
routes what you hear through an effects sink (EasyEffects, Carla, a virtual
mixer) while the system default output is the raw device underneath, every app
that just opens the default plays where you cannot hear it — correctly, and
inaudibly. Pick that sink here and the alarm follows you instead of the default.
Sound check now names the device it played to, so "I hear nothing" becomes "it
played on X, and X is not what I am listening to".

Zoom the selector. A three-pixel target on a 4K screen shown in a 700px
preview cannot be selected at all — one preview pixel covers six screen pixels.
Now:

• Zoom to 16× with Ctrl+scroll (anchored at the pointer), the +/−/Fit buttons,
  and middle-drag to pan.
• A magnifier follows the cursor, showing the source frame's real pixels at 10×
  with a crosshair on the exact pixel under it.
• Arrow keys nudge the rectangle one screen pixel at a time; Shift resizes the
  far edge, Alt jumps ten.
• The region readout gained its origin in source pixels.