React Tree

Provide an option to see departments either as a list (as now), or as a tree. The tree expands to show related sub departments, as links. If I click on the dept name link, then open the department "show" to the right.

TECHNICAL CONSTRAINTS:

• Avoid recursion stack overflow: include proper termination conditions
• Handle mixed data types: use parseInt() for ID comparisons
• Prevent import conflicts: use aliases for Material-UI components
• Verify data relationships: check actual field names in backend
• Use incremental development: start simple, add complexity gradually
• Test each layer: tree logic → expansion → detail panel → tabs