Fix base manifest asset sync

[ghost]

Summary

• allow asset sync to resolve manifest resources for base device variants ()
• cover K850-style manifests whose uses a device-specific filename such as
• keep extended variant lookup behavior covered by a regression test

Root cause

The sync path downloaded , then skipped manifest resource lookup whenever the connected device reported . Some depots do not provide a generic / baseline and instead reference the base image only through , so those devices could keep showing the placeholder even though their image existed in the asset index and on the asset server.

Validation

• started after downloading dependencies, but could not complete locally because requires Apple's missing Metal Toolchain ().