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/messages/en.json

@@ -207,7 +207,12 @@
     "widgetImportantTasks": "Important Tasks",
     "widgetPendingConnections": "Pending Connections",
     "widgetSeats": "Seat Usage",
-    "widgetPendingStaffInvites": "Pending Staff Invites"
+    "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…",