NX Sentry 0.1.0

First release.

Pick a screen or a window, drag a rectangle over the part of it you care about,
and NX Sentry sounds an alarm when the pixels inside that rectangle change.

• Four synthesised alarms (siren, beep, pulse, chime) with volume control, an
  optional desktop notification and a taskbar flash. Nothing to install, no
  audio files to ship.
• Guards against false alarms: a grace period after arming, N consecutive
  frames over the threshold before it fires, and a quiet time after each alarm.
• A live meter of how much of the area is moving against the threshold that
  would trip it, a marker on the preview showing what moved, and a timestamped
  log of every trigger.
• Closes to the tray and keeps watching; the tray menu arms, disarms and
  silences.
• Wayland capture goes through xdg-desktop-portal, so the compositor decides
  what may be seen — and when a share is revoked the sentry disarms itself
  instead of pretending to watch a dead stream.

Nothing leaves the machine: frames are compared and thrown away, and the app has
no network code at all.

Linux x86_64 AppImage. On distributions without libfuse2 (CachyOS among
them) run it via NX Hub, or extract it with --appimage-extract.

Verify the download against nx-sentry-0.1.0-linux-x86_64.AppImage.sha256; the
.sig sidecar is ed25519 over that digest with the NX release key NX Hub pins.