Astroshot capture

Native archdev shots support

When archdev shots is available and enabled, the same engine runs as a command group of archdev. Detect it once per session:

if command -v archdev >/dev/null 2>&1 && archdev shots doctor >/dev/null 2>&1; then
  NATIVE=1   # archdev shots is installed and enabled
else
  NATIVE=0   # use the standalone astroshot commands in this skill
fi

archdev shots doctor exits 0 only when the feature is installed and enabled (archdev settings set shots on). Any other result means: use the standalone astroshot commands below, which stay the fallback.