Evaluate workflow logic with portable, serializable expressions

Workflow Condition, Loop, and Router steps now support CEL (Common Expression Language) evaluators. Expressions are defined as strings, making workflows fully serializable and easier to store, review, and move across environments.

This change improves portability and governance for teams managing workflows as configuration rather than code. CEL provides a consistent, readable way to express branching and decision logic without embedding runtime objects, reducing coupling and deployment risk.

Why this matters

Easier workflow versioning and auditing
Improved portability across environments and runtimes
Less friction when storing workflows in configuration or policy systems