The previous commit indexed custom-URL satellites under "Other", which is the key manual
file import already writes. setSatelliteTypeIds overwrites rather than merges, so importing
a file and then updating from a custom URL erased each other's type index - a probe
confirmed it in both directions.
The satellites were never at risk: database rows survive because insertEntries is REPLACE
with no delete, and the selection is a separate id list. What was lost was their grouping in
the type filter. Still worth a distinct key, since a URL and a hand-picked file are
different things.
Custom URLs now use "Custom". Manual import keeps "Other". The test asserts the new key and
that "Other" stays untouched, so the collision cannot come back unnoticed.