NX Sentry 0.2.0

Watching literal pixels.

Sensitivity multiplier — ×1 to ×1000 on a geometric slider, dividing both
detection thresholds. Past roughly ×8 the brightness threshold reaches zero: a
change of one unit counts, and the area threshold falls below a single pixel of
any realistic region.

Pixel-exact mode — the region is analysed at 1:1 instead of a 192px
thumbnail, and compared colour channel by colour channel instead of by
brightness. Both halves matter: a downscale averages one changed pixel into its
neighbours, and greyscale maps different colours onto the same luma, so a pixel
that changes colour without changing brightness is invisible without it. The
detection panel says which case it is in — 1:1, downscaled, or capped for a
region past 4 megapixels — rather than implying an exactness it is not
delivering.

Minimum changed pixels — an absolute floor ANDed with the area threshold, so
a boosted setup does not fire on one stray pixel of video noise. At 1 it is a
no-op and a single changed pixel is a trigger.

The meter and the log now read in pixels as well as percent, because at a high
multiplier the percentage is all zeroes and the only readable number is how many
pixels moved.

Also: NX_SENTRY_CONFIG_DIR now redirects Electron's own userData, so a test
run can no longer take the single-instance lock from an installed copy.

Verify the download against the .sha256 sidecar; the .sig is ed25519 over
that digest with the NX release key NX Hub pins.