refactor: reuse existing earnings/sales service functions in dashboard

Commit notes

- Import and use getCreatorEarningsSummary instead of direct DB query - Import and use getCreatorRecentSales instead of duplicate getRecentSales - Keep dashboard-specific functions (getSalesChartData, getTopPacks) that don't exist elsewhere - Add helper functions for published pack count and Pro subscription check

Co-authored-by: armin.naimi <[email redacted]>