Feature: Support Output Converter Selection in Activity Output Bindings

## Depends On

Requires support for the proposed **[Extensible Activity Output Converters](https://github.com/elsa-workflows/elsa-core/issues/7770)** capability within Elsa Core.

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## Summary

If output converter support is introduced in Elsa Core, workflow designers should be able to configure output conversions directly within Elsa Studio when binding activity outputs to workflow variables.

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## Problem

Currently, activity outputs can be bound to variables, but there is no way to optionally transform the output value during the binding process.

This means workflow authors must either:

- Use custom activities.
- Add transformation steps.
- Handle conversion logic manually later in the workflow.

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## Proposed Enhancement

Extend the Output configuration experience to support optional converter selection.

Conceptual example:

```text
Output:
Result
|
+--> Variable: QueryResults
+--> Converter: DataSetToRecordCollection
```

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## Desired Behaviour

When converter support is available:

- Converter selection should remain optional.
- Existing workflows should continue functioning unchanged.
- Available converters should be discoverable from registered converter providers.
- Converter configuration should integrate naturally into the existing Output experience.

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## Additional Notes

While investigating this feature, it appears that the Output tab may not currently expose the same extensibility mechanisms used elsewhere through Field Extensions.

If output converter support is approved, this may provide a good opportunity to introduce an extension point for output binding configuration.

The issue names no files or tests. Start by reviewing the existing Output tab and the Field Extensions mechanisms, then confirm the dependency in Elsa Core issue #7770. Done means optional selection from registered converters, unchanged existing workflows, and integration into the existing Output experience.

Written by the indexing model from the issue text.