Add Today dashboard foundation with permission-aware KPI summary API.

Replace hardcoded Today cards with a backend summary endpoint and composable frontend widgets filtered by org type and tab permissions.

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

frontend/messages/en.json

@@ -194,10 +194,20 @@
     "noSubscriptionNotice": "This organization does not have an active subscription yet.",
     "choosePlanLink": "Choose a plan",
     "noSubscriptionCta": "to start the purchase process.",
-    "cardTodaysAppointments": "Today's Appointments",
-    "cardActivePatients": "Active Patients",
-    "cardNewLabCase": "New Lab Case",
-    "cardTodayInvoices": "Today invoices"
+    "noWidgets": "No dashboard metrics are available for your current permissions.",
+    "loadError": "Could not load dashboard metrics.",
+    "seatsUnlimited": "Unlimited plan",
+    "widgetAppointmentsToday": "Today's Appointments",
+    "widgetPatientsToday": "Patients Today",
+    "widgetTreatmentsToday": "Treatments Today",
+    "widgetDraftTreatments": "Draft Treatments",
+    "widgetLabCasesPendingSend": "Lab Cases Pending Send",
+    "widgetCasesReceivedToday": "Cases Received Today",
+    "widgetTasksInProgress": "Tasks In Progress",
+    "widgetImportantTasks": "Important Tasks",
+    "widgetPendingConnections": "Pending Connections",
+    "widgetSeats": "Seat Usage",
+    "widgetPendingStaffInvites": "Pending Staff Invites"
   },
   "staff": {
     "redirecting": "Redirecting…",