PM-5719: Add member payment dashboard data

[jmgasper]

What was broken

The Reports Portal API returned only the original dashboards, so it could not supply monthly member payment values by type or by customer.

Root cause

There were no dashboard SQL queries, DTOs, service mappings, or export paths for the two member payment datasets.

What was changed

• Added zero-filled monthly member payment totals split across TAAS, Task, Contest, and Engagement buckets.
• Added the selected range's top five clients as stable series and grouped remaining or unnamed clients under Other Customers.
• Added both datasets to aggregate, detail, and CSV endpoints with Swagger metadata and README documentation.
• Reused the existing paid-event, latest-version, member-amount, customer, and half-open UTC range conventions.

Any added/updated tests

• Added SQL structure coverage for payment categorization, latest versions, customer joins/ranking, and Other Customers.
• Updated service and controller coverage for numeric mapping, zero filling, aggregate/detail responses, and CSV exports.
• PM-5719 focused tests pass: 5 suites and 35 tests.
• pnpm lint and pnpm build pass. The full repository suite was also run; 3 unrelated SFDC/report-directory suites fail on unchanged code paths, while 19 suites and 338 tests pass.