feat(export): generate and download CSV reports

[Bogdan2005-19]

📝 Description (User Story)

As a data scientist,
I want to export the requested information in a CSV file format via direct download
so that I can perform external strategic analysis using the universal standard format.

🔗 Epic / Parent Issue

Part of: #17

✅ Acceptance Criteria (Fit Criteria)

• When requesting the export, the system gathers the filtered information and structures it into a ready-to-use CSV file.
• Pressing the "Generate .CSV" button forces the file download to the actor's computer.
• The file includes the content name, favorites count, and views per platform.
• All date fields in CSV files must follow the ISO 8601 format: YYYY-MM-DD.

🛠️ Technical Checkpoints / Tasks

• Implement backend logic to convert database arrays to comma-separated text format.
• Configure the HTTP response headers to force a file download.
• Implement date formatting logic in the CSV export module.