Add Recharts bar charts to Today dashboard summary.

Extend the Today summary API with treatment mix and workflow task breakdowns, and render permission-aware chart cards on the Today page using Recharts.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/scripts/build-messages.mjs

@@ -200,6 +200,11 @@ const en = {
     widgetPendingConnections: 'Pending Connections',
     widgetSeats: 'Seat Usage',
     widgetPendingStaffInvites: 'Pending Staff Invites',
+    chartTreatmentMixTitle: 'Treatment Mix',
+    chartTreatmentMixSubtitle: 'Last 7 days',
+    chartTasksByStepTitle: 'Tasks by Workflow Step',
+    chartTasksByStepSubtitle: 'In progress now',
+    chartEmpty: 'No data for this period yet.',
   },
   staff: {
     redirecting: 'Redirecting…',