Add data export functionality

[larralapid]

Description

Implement data export features to allow users to backup and use their expense data in other applications.

Export Features

• CSV export for all receipts
• PDF receipt summaries
• Monthly/yearly expense reports
• Category-based exports
• Date range filtering for exports

Technical Requirements

• CSV generation with proper formatting
• PDF generation for reports
• File sharing integration
• Email export option
• Data filtering and formatting

Priority: Medium

Important for user data portability and backup purposes.