feat: condition node functionality with CEL evaluation in Workflows (#2280)

* feat: add condition node functionality with CEL evaluation

- Introduced ConditionNode to support conditional branching in workflows.
- Implemented CEL evaluation for state updates and condition expressions.
- Updated WorkflowEngine to handle condition nodes and their execution logic.
- Enhanced validation for workflows to ensure condition nodes have at least two outgoing edges and valid expressions.
- Modified frontend components to support new condition node type and its configuration.
- Added necessary types and interfaces for condition cases and state operations.
- Updated requirements to include cel-python for expression evaluation.

* mini-fixes

* feat(workflow): improve UX

---------

Co-authored-by: Alex <a@tushynski.me>

frontend/src/agents/workflow/nodes/BaseNode.tsx

@@ -5,7 +5,7 @@ interface BaseNodeProps {
   title: string;
   children?: ReactNode;
   selected?: boolean;
-  type?: 'start' | 'end' | 'default' | 'state' | 'agent';
+  type?: 'start' | 'end' | 'default' | 'state' | 'agent' | 'condition';
   icon?: ReactNode;
   handles?: {
     source?: boolean;
@@ -40,6 +40,9 @@ export const BaseNode: React.FC<BaseNodeProps> = ({
   } else if (type === 'state') {
     iconBg = 'bg-gray-100 dark:bg-gray-800';
     iconColor = 'text-gray-600 dark:text-gray-400';
+  } else if (type === 'condition') {
+    iconBg = 'bg-orange-100 dark:bg-orange-900/30';
+    iconColor = 'text-orange-600 dark:text-orange-400';
   }
 
   return (