feat: drag-and-drop employee reordering

[trinnode]

Closes #68

Description

Implemented drag-and-drop reordering for the employee management table using @dnd-kit.

Technical Approach

• UI/UX: Added a dedicated drag handle column so text selection in other columns remains unaffected.
• State Management: Implemented optimistic UI updates via @tanstack/react-query. The table reorders instantly on drag end, preventing layout flicker.
• Security & Performance: The API payload is minimized to send only { id, newIndex } instead of full employee objects. Added automatic rollback to the previous cache state if the mutation fails.
• Accessibility: Drag handles are keyboard navigable with tabIndex={0} and proper aria-labels.

Screenshots/Screen Recording

*

Checklist

• Tested optimistic updates and API failure rollbacks
• Keyboard accessibility tested
• All 19 Vitest suites passing
• npm run lint and npm run build pass locally

[Wilfred007]

Hi @trinnode there seem to be a merge conflict, do well to resolve it in good time so I can test and merge your pr. thank you

[Wilfred007]

[Wilfred007]

Hi @trinnode kindly resolve conflicts and let me know, thank you

[trinnode]

Hello @Wilfred007 I have resolved the conflicts. Thank you

[trinnode]

Please ensure these are installed in the target app where this feature is merged:

Runtime:

@dnd-kit/core
@dnd-kit/sortable
@dnd-kit/utilities

and reference the new files in App.tsx

import EmployeeTable from "./pages/EmployeeTable";

  <NavLink
              to="/employees"
              className={({ isActive }: { isActive: boolean }) =>
                `text-sm font-medium ${isActive ? 'text-blue-600' : 'text-gray-500 hover:text-gray-700'}`
              }
            >
              Employee Table
            </NavLink>```
            
           Then also include it in the route
           @Wilfred007 

[trinnode]

Hello @Wilfred007 , Please merge my PR