ngmix v2.0: one column grammar across estimators (PSF source-of-truth, single size, E↔G) #777

Sub-issue of the ngmix v2.0 epic (#762). Turns the PSF-column tangle that surfaced in #741 into one column grammar for the whole catalogue: every shape estimator the pipeline writes — ngmix, HSM moments, galsim — names its outputs ESTIMATOR_COMPONENT_OBJECT[_metacaltype] (uppercase), with a single size definition (T = 2σ², sourced once from cs_util.size), ellipticity split into named scalar components with the e-type/g-type distinction made correct everywhere, GAL dropped, and spread_model removed.

This is the card for the work; the implementation rides the Development link below.

Implemented by: PR #761 (branch refactor/psf-column-grammar, base ngmix_v2.0) — mergeable, CI green. Depends on cs_util.shape (e↔g converters, #768 / cs_util#73) and cs_util.size.

Closes #761 is not used (the PR targets ngmix_v2.0, not the default branch); the Development link binds them on the board, and the chain auto-closes this issue when it reaches develop.

— Claude on behalf of Cail