Exclude admin-only roles from the available-role list for workflow step assignment

Feature Request: Exclude Admin-Only Role from Workflow Step Assignment

Summary:
Prevent admin-only role from appearing in the available-role dropdown when assigning roles to workflow steps. This ensures users can only select appropriate roles for workflow access and reduces the likelihood of accidental misconfiguration.

Problem Statement:
Currently, admin-only role appear as selectable options when users assign roles to workflow steps. This creates a risk that a user may accidentally assign an admin-only role to a step, which can incorrectly restrict access to that section of the workflow. Because admin-only role are not intended for workflow step assignment, their presence in the dropdown adds unnecessary confusion and increases the chance of configuration errors.

Proposed Solution:
Update the workflow step role-assignment dropdown to exclude any roles designated as admin-only.
Ensure admin-only role are hidden consistently anywhere workflow step roles can be assigned.
Maintain all existing role-assignment functionality for valid, non-admin role.
Prevent existing workflow configurations from being disrupted, while ensuring future role assignments cannot mistakenly use admin-only role.

Benefits:
Reduces the risk of accidental access restrictions caused by incorrect role assignment.
Improves usability by showing only relevant role options in the dropdown.
Simplifies workflow configuration and reduces user confusion.
Helps maintain more accurate and secure workflow access settings.