Add total revenue calculation and display for paid events

[stefan-burke]

Summary

This PR adds revenue tracking functionality to the admin events page, allowing event organizers to see the total revenue generated from ticket sales.

Changes

• New calculateTotalRevenue function: Computes total revenue in cents from attendees by:

  • Summing price_paid values when available
  • Falling back to unit_price * quantity for attendees without explicit pricing
  • Handling edge cases like null unit prices and non-numeric price values

• New formatRevenue helper: Converts cents to a human-readable decimal format (e.g., 1000 cents → "10.00")

• UI enhancement: Displays total revenue on the admin event details page, but only for paid events (when unit_price is not null)

• Comprehensive test coverage: Added 11 new tests covering:

  • Empty attendee lists
  • Price paid summation
  • Unit price fallback calculation
  • Mixed pricing scenarios
  • Invalid/missing data handling
  • UI rendering for both paid and free events

Implementation Details

• Revenue is stored and calculated in cents to avoid floating-point precision issues
• The calculation gracefully handles missing or invalid price_paid values by falling back to the unit price calculation
• The revenue display is conditionally rendered only for events with a defined unit price, keeping the UI clean for free events

https://claude.ai/code/session_013tY9Yv4MsSbzieu8LS89aR