EXIF Orientation only knows 0/90/180/270, so a library still carries no
record of how the camera was held. The sensor had nothing to offer.
AUTO now measures the dominant line in the picture itself:
src/utils/horizon.ts runs a shear-projection search (coarse 1 deg over
-45..45, then a 0.5 deg refine) on a <=256px thumbnail, bails when no
line's score beats 3x the median, and returns the tilt in degrees.
App applies photoStraighten = -tilt, so preview and export share one
number exactly as the slider did.
Removes expo-sensors wiring, the horizonRoll state, effectiveStraighten
and the bubble-level overlay (autoRoll prop) from App/AdjustmentPanel/
Viewfinder. expo-sensors stays in package.json.
