ingest_photometry function should take asymmetric errrors

Right now, ingest_photometry function expects symmetric errors but it should optionally accept asymmetric errors.

At this point, we're telling the ingest_photometry SKILL to just do this itself, but adding it to the function would be better in the long run. (token conservation.)

Start by locating the ingest_photometry function and its tests, then compare how symmetric errors are currently handled. The work is done when the function optionally accepts asymmetric errors while preserving existing symmetric-error behavior, with tests covering both forms.

Written by the indexing model from the issue text.