Enable remote signing for federated catalogs

### Is your feature request related to a problem? Please describe.

PR #2280 introduces support for remote signing.

Currently, this new, experimental feature is restricted from use with federated catalogs. This limitation is in place to minimize the "blast radius" while the feature is being hardened and tested.

But the plan is to eventually extend remote signing to federated catalogs, gated by a feature flag.

### Describe the solution you'd like

_No response_

### Describe alternatives you've considered

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### Additional context

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Start by reviewing PR #2280 and the current code that restricts remote signing for federated catalogs. Trace how the existing experimental feature flag is applied and identify the federated-catalog path that must be enabled. Done means remote signing works for federated catalogs behind a feature flag without removing the experimental guard.

Written by the indexing model from the issue text.