Make the edit path symmetric with upload: model_type: is an operational
placement tag on a model asset, so an unregistered folder_name is an invalid
placement target and is rejected (400 UNKNOWN_MODEL_TYPE), not stored as a
label. A real edit-type action always targets a registered folder from
discovery, so only junk manual adds are affected.
Narrowly update the system-looking-labels test to drop the now-operational
bare model_type: case (other reserved-ish prefixes still store as labels) and
add a focused unknown-model_type:-on-model-asset rejection test.
5e267faf02