Implement CSV and JSON export functionality for dashboard data

[deedee-code]

Summary

Added client-side dashboard export support for current positions and event history in both CSV and JSON formats. The export buttons are now available in the dashboard header, and downloads are generated entirely in-browser without any server round-trip.

Related Issue

Closes #13

Checks

• I read the contribution guide.
• I kept this pull request scoped to the linked issue.
• I ran the relevant local checks or explained why they were skipped.
• For Drips wave issues, I claimed the issue before opening this pull request.

Notes for Reviewers

• Export buttons were added to dashboard.ts.
• Export payload construction and download logic were implemented in dashboard.screen.ts.
• CSV and JSON outputs contain the same position/event history data structure.
• Filenames use the wallet address prefix and current ISO date.
• The implementation is fully client-side and does not call any server endpoint.

[drips-wave]

@deedee-code Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits