feat: implement complete invoicing application with CSV import and PDF export

- Add comprehensive CSV import system with drag-and-drop upload and validation
- Create UniversalTable component with advanced filtering, searching, and batch actions
- Implement invoice management (view, edit, delete) with professional PDF export
- Add client management with full CRUD operations
- Set up authentication with NextAuth.js and email/password login
- Configure database schema with users, clients, invoices, and invoice_items tables
- Build responsive UI with shadcn/ui components and emerald branding
- Add type-safe API layer with tRPC and Zod validation
- Include proper error handling and user feedback with toast notifications
- Set up development environment with Bun, TypeScript, and Tailwind CSS

src/components/ui/toaster.tsx

@@ -0,0 +1,8 @@
+// Copied from shadcn/ui documentation
+
+import * as React from "react"
+import { Toaster as Sonner } from "sonner"
+
+export function Toaster() {
+  return <Sonner richColors position="top-center" />
+}