Add charts to the XLSX playground sample

[naaiyy]

Summary

• replace the small workbook fixture with the verified event-revenue workbook
• show a projected-versus-actual chart and an actual-revenue pie chart in the existing XLSX sample
• exercise the multi-area category reference that the chart refactor now supports

Verification

• playground tests pass
• playground type check passes
• playground production build passes
• manual browser verification confirms both charts are visible with all six categories and correct values