Gradient tool handles desync from exposed Fill gradient chains

When a Gradient Value node feeds an exposed Fill node, the rendered gradient uses Fill's bounding box derived transform, but the Gradient tool reads identity from the chain until a Transform node is materialized. The metadata of the Fill node is also used for the chain.

https://github.com/user-attachments/assets/9b2c92ff-6097-4846-b7bd-4d05a19bada6

Reproduce the case shown in the attached recording: connect a Gradient Value node to an exposed Fill node and compare the rendered gradient with the Gradient tool handles. Trace how the Fill bounding-box-derived transform and node metadata are used before a Transform node is materialized; done means the handles and rendered gradient stay aligned through that chain.

Written by the indexing model from the issue text.