Add CSV export functionality to invoices page

[devin-ai-integration]

Add CSV export functionality to invoices page

Summary

Adds a client-side CSV export feature to the invoices page that allows users to export their currently filtered invoice data. The implementation includes:

• Export button placed next to "New Invoice" with Download icon from lucide-react
• Filtered export that respects current search term and status filter selections
• CSV format with proper headers, quoted customer names, formatted dates (YYYY-MM-DD), and decimal amounts
• User feedback via toast notifications for success, warning (no data), and error states
• Client-side download using Blob API with filename including current date

Review & Testing Checklist for Human

• Filter behavior: Test export with search filter active and status filter active to verify only filtered invoices are exported
• CSV content validation: Open downloaded CSV to verify correct headers, quoted customer names, date formatting (YYYY-MM-DD), and decimal amounts
• Edge cases: Test export with no invoices (should show warning toast), and with invoices containing special characters in customer names
• UI/UX: Verify Export button appears correctly next to New Invoice, toast notifications display properly, and download triggers in browser

Recommended Test Plan

1. Navigate to /invoices page
2. Test export with no invoices → should show "No invoices to export" warning
3. Create test invoices with various customer names (including commas, quotes)
4. Test export with all invoices → should download CSV and show success toast
5. Apply search filter, test export → should only export matching invoices
6. Apply status filter, test export → should only export matching invoices
7. Open downloaded CSV files to verify content format

Notes

• Uses manual CSV generation (not a library) - watch for edge cases with special characters
• Relies on existing filteredInvoices state from search/filter logic
• Client-side approach avoids backend changes but may have memory limitations with large datasets

Requested by: @JRWu
Link to Devin run: https://app.devin.ai/sessions/de7e56118cac410bbcf3752c570aa1ee

[devin-ai-integration]

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[sonarqubecloud]

Quality Gate failed

Failed conditions
B Maintainability Rating on New Code (required ≥ A)

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