Galaxy selection: replace the IMAFLAGS_ISO == 0 cut with a MASK_r bit cut once ShapePipe consumes healsparse masks

classification_galaxy_base keeps objects with IMAFLAGS_ISO == 0.
That column carried the tile-level ShapePipe mask (GSC star halos, spikes, Messier/NGC) and was the only place bright-star masking reached the galaxy sample.
After CosmoStat/shapepipe#847 ShapePipe no longer generates masks and tile detection runs without a flag image, so IMAFLAGS_ISO is absent from the final catalogue.
Instead, every UNIONS healsparse mask bit is queried per object and written as MASK_<band> columns (bit table: wiki).

Needed here: the galaxy cut becomes (MASK_r & BITS) == 0 with a configured bit set — the natural default is halos + star + manual + MaxiMask (bits 0, 1, 2, 3, 10), the same combination as the cumulative area table on the wiki page.
The instrument flags stay available per epoch through ngmix's epoch handling; nothing else in the selection changes.

Not urgent: only after #847 (and its base #852) merge and the first catalogues with MASK_<band> columns exist.

— Claude on behalf of Cail

Locate the galaxy-selection code containing classification_galaxy_base and inspect how the IMAFLAGS_ISO cut is configured and tested. Review the MASK_r bit mapping in the linked wiki and wait for #847/#852 and catalogues with MASK_ columns. Done means the selection uses the configured halos, star, manual, and MaxiMask bits while leaving other selection behavior unchanged.