Add dedicated permission for entity-context session creation

Summary

Implement a dedicated permission for creating entity-context playground sessions via the API. This provides fine-grained access control allowing site administrators to control who can programmatically create entity-aware workflow sessions separately from general playground access.

Business Value

• Enables granular access control for API-based session creation
• Allows restricting programmatic access while maintaining UI access
• Supports compliance requirements for controlled API access
• Provides flexibility for role-based permission configuration

Features Implemented

• New Permission: "Create entity-context playground sessions via API"
• Restricted Access: Permission marked as restricted for security
• API Protection: Applied to REST API endpoints
• Complementary to Existing: Works alongside standard playground permissions

Technical Implementation

• Permission defined in flowdrop_node_session.permissions.yml
• Permission key: create entity context sessions
• Applied to API routes via routing configuration
• UI routes continue to use create flowdrop_playground_session permission

Permission Configuration

create entity context sessions:
  title: 'Create entity-context playground sessions via API'
  description: 'Allows creating playground sessions with entity context through the REST API'
  restrict access: TRUE

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