final_cat.param requests IMAFLAGS_ISO that the unmasked tile chain never produces; sp_validation cuts on it

[cailmdaley]

workflow/config/cfis/final_cat.param lists IMAFLAGS_ISO, but the committed tile detection runs with FLAG_IMAGE = False and default_noimaflags.param (config_tile_Sx.ini), so no tile catalogue carries the column and merge_final_cat reads one that is never there. Downstream, sp_validation's classification_galaxy_base cuts on IMAFLAGS_ISO == 0, so the v2 catalogue either fails that selection or the cut has to move to the healsparse MASK_<band> columns. This is the object-level half of the masking decision (the pixel-level half — epoch flag source — is settled). Decide: drop IMAFLAGS_ISO from final_cat.param and port sp_validation's cut to MASK_<band>, or re-enable tile flag images. Recorded as a [LINT] on detection.detection_source_mode in astra.yaml (#875).