Enhance: Create premium Child Item modal with full feature parity

Added comprehensive CreateChildTaskModal component with all premium features
from CreateWorkItemModal including duplicate name detection, animated status
dropdown, visual priority selector, tags input, contributor assignment, and
due date picker. Updated terminology from "Child Task" to "Child Item" to
reflect support for all work item types. Fixed TypeScript type errors in
WorkItem interface and resolved all ESLint warnings with proper type
definitions and commented error handlers.

Additional improvements:
- Changed default relationship type to DEPENDS_ON in CreateWorkItemModal
- Added readOnly mode to WorkItemDetailsModal for view-only scenarios
- Updated tooltip text to "Create child item" in graph visualization

Author: Patel230