fix(frontend): restrict source target workflow conversational type only

[yassinedorbozgithub]

Summary:
Restricted source-target workflow selection in the frontend to only allow workflows with the conversational type. This prevents unsupported workflow types from being displayed or selected in source-target workflow configurations.

Why:
Source-target workflows are designed to work exclusively with conversational workflows. Allowing other workflow types could lead to invalid configurations, unexpected behavior, or user confusion.

How to review:
Focus on the source-target workflow selection and filtering logic in the frontend. Verify that only workflows with the conversational type are available for selection and that non-conversational workflows are excluded from the UI.

Validation:

• Verified that conversational workflows continue to appear and can be selected.
• Confirmed that non-conversational workflow types are no longer displayed in source-target workflow selectors.
• Checked that existing source-target workflow flows behave as expected after the change.