[FE-62] Implement dashboard widget customisation — drag-to-reorder and show/hide cards

[yusuftomilola]

Overview

The dashboard currently shows a fixed set of summary cards and charts. Different users care about different metrics — a MANAGER wants to see their department's maintenance schedule while a USER wants quick access to their assigned assets. Allowing personalisation improves the relevance of the dashboard for every role.

Context

• Dashboard page: frontend/app/(dashboard)/dashboard/page.tsx
• dnd-kit is already installed and can power drag-and-drop card reordering
• User preferences (widget order and visibility) should be stored in localStorage keyed by user.id
• The set of available widgets: Summary Stats, Assets by Status chart, Assets by Category chart, Recent Assets table, Upcoming Maintenance, My Assigned Assets, Low Stock Alerts, Overdue Checkouts

Acceptance Criteria

• Add a "Customise Dashboard" button to the dashboard header
• Clicking enters "edit mode": widgets display a drag handle and an eye/hide toggle
• Drag-and-drop reordering using dnd-kit useSortable; the layout updates live as cards are dragged
• Hiding a widget removes it from the dashboard but adds it to a "hidden" list in the customise panel
• "Done" saves the layout and visibility to localStorage and exits edit mode
• "Reset to Default" restores the original widget order and visibility
• The saved layout is loaded on every dashboard visit; the dashboard renders in the user's last configured order