Issue #62 — Data export (admin)

[GoSTEAN]

Title: [Admin] Implement data export endpoints for compliance

Tags: backend, admin, feature, security

Description:
Allow admins to export user, trade, and financial data as CSV for regulatory compliance and reporting.

Acceptance Criteria:

• GET /admin/export/users — CSV of all users (id, email, joinedAt, kycStatus, walletAddress).
• GET /admin/export/trades?from=&to= — CSV of all trades in date range.
• GET /admin/export/treasury — CSV of all fee collection events.
• Exports streamed (not buffered) to handle large datasets.
• Requires admin auth + audit log entry per export.
• Async export for large ranges: POST /admin/export/request → emailed when ready.

Files: src/routes/admin.routes.ts, src/services/export.service.ts

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