An invoicing app. Create an invoice with: client name + email, line items(description + qty + unit price), tax rate, due date, notes. Calculatetotal automatically.Generate a PDF (use react-pdf or html-to-pdf). Email it to the client viaResend. Track status (draft / sent / paid / overdue). Mark paid manuallyOR via Stripe payment link.List view of all invoices, sortable by date or status, searchable by client.