CLAUDE: 3-A3 fix - pure border-ring interior gate (morphological shrink annihilated the patchy selection)

First attempt (8fb0eea4) shrank the finite-calibration mask morphologically -
but the calibration is NaN wherever a tile was not STRENGTH-selected (whole sky
+ scattered terrain holes, ~21% finite density), so a 2-tile 8-dir shrink left
~2 tiles per scene: num=2 fits, dstored 6-10 px, LMA failures (07/13 run,
killed). Andrey's ruling: pure border ring - the OOB-missing band is
geometrically confined to the frame border (margin-dropped ring 1-2 tiles +
partial-OOB soft band 12 px = 1.5 tiles), so excluding tiles within
curt.pose_shrink (default now 4) tiles of the array border covers
hard+soft+slack with zero collateral on interior strength holes. No TileNeibs,
no morphology. Dialog label now "Pose tile selection border ring (tiles)";
key _curt_pose_shrink unchanged.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>