Add WorkItemTypeCreate GraphQL mutation

Issue: [BE] Create workItemTypeCreate mutation (#581937 - closed)

What does this MR do and why?

This merge request adds a new feature to create custom work item types. The changes introduce a GraphQL mutation called workItemTypeCreate that allows users to create new work item types with custom names and icons.

The feature includes:

• A new API endpoint for creating work item types with validation for required fields like name and optional icon selection
• Support for creating types at both the group level (for root groups only) and organization level
• A set of predefined icons that users can choose from (like bug, epic, feature, task, etc.)
• Proper permission checks to ensure only authorized users (maintainers and owners) can create custom types
• Error handling for invalid inputs and unauthorized access attempts

References

• [BE] Create workItemTypeCreate mutation (#581937 - closed)
• Add WorkItemTypeUpdate GraphQL mutation (!223505 - merged)

Screenshots or screen recordings

With a full_path
Without a full_path
Duplicate Name in same namespace
With FF disabled
Invalid Icon Name

How to set up and validate locally

1. Turn on the FF work_item_configurable_types.
2. Execute the mutation with fullpath (creates the type at group level)/ without fullpath (creates for current organization).

mutation {
  workItemTypeCreate(input: {
    fullPath: "your-group-path"
    name: "Custom Bug Type"
    iconName: "bug"
  }) {
    workItemType {
      id
      name
      iconName
    }
    errors
  }
}

3. Ensure that the custom work item types were persisted in the database with the correct organization_id/namespace_id
4. In the rails console check

  bin/rails c

  WorkItems::TypesFramework::Custom::Type.last

  => #<WorkItems::TypesFramework::Custom::Type:0x0000000147af6a98
  id: 1001,
  created_at: "2026-02-18 04:44:00.818292000 +0000",
  updated_at: "2026-02-18 04:44:00.818292000 +0000",
  organization_id: nil,
  namespace_id: 143,
  icon_name: "bug",
  converted_from_system_defined_type_identifier: nil,
  name: "Custom Bug Type">

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.