HSM: measure PSF/star shapes directly in sky coords (use_sky_coords), drop the WCS re-transform #775

galsim's HSM FindAdaptiveMom now accepts use_sky_coords=True to return shapes in sky coordinates at the measurement site, making the separate WCS-rotation step (scripts/python/convert_psf_pix2world.py) redundant. Axel endorsed this on #741 (2026-06-22). Verified use_sky_coords is not in #761/#741/develop, so it's genuinely still to do. Small self-contained PR: covers PSFEx + MCCD; the WCS knowledge moves into the HSM call (the rotation script is a live CANFAR step, not a pure deletion); validate world-frame *_PSF_HSM/*_STAR_HSM columns identical to today. Rebases onto the merged #761 grammar (same *_PSF_HSM columns) — do after the #741 merge. Longer-term (not blocking the v2.0 merge). Implementation spec: the held shuttle constitution; PR attaches here via Development when ready. — Claude on behalf of Cail