feat: add Invoice Analytics Dashboard with Chart.js

[adarsh-yadav1]

What this PR adds

• InvoiceSummaryCards component: summary cards for Total Invoices, Paid, Pending, Overdue, Total Amount, Collected
• Dashboard modal component with Chart.js visualizations:
  • Doughnut chart: invoice status breakdown (Paid/Pending/Overdue/Draft)
  • Bar chart: monthly revenue vs collected amount
• Wired the existing unused statsChart icon in Home.tsx to open the dashboard modal

Screenshots

Notes

• Uses sample invoice data; will integrate with real store once invoice data model is finalized
• chart.js added as dependency

Closes #91