Add cumulative time series with timeframe filter to all statistics pages

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

docs/statistics.md

@@ -15,6 +15,10 @@ Statistics pages live under `/stats/*` (`src/frontend/src/views/StatisticsView.t
 | `GET /api/stats/managed` | any user (own orders only) | Order Management |
 | `GET /api/admin/stats` | site admin | Site Overview |
 
+## Time series
+
+Every page has an "Over time" panel (`TimeSeriesPanel.tsx`): cumulative charts with a timeframe filter (1W, 1M, 3M, 1Y, YTD, All, custom range). Running totals start at 0 at the start of the timeframe. Site-wide daily counts come from `daily` in `/api/admin/stats`.
+
 ## My Orders (orderees)
 
 - ✅ Participation over time (orders joined per month) and current streak (consecutive weeks)