fix(pos): clamp payment amount to total + allow 1c tolerance for rounding

backlog/features.json

@@ -8192,6 +8192,22 @@
       },
       "phase": "pos",
       "completed_at": "2026-08-26T20:58:39Z"
+    },
+    {
+      "id": "POS-PAYMENT-OVERPAY-FIX",
+      "type": "bug",
+      "title": "POS selfpay: payments exceed total",
+      "description": "In selfpay flow, after selecting payment method the frontend reports payments exceed total. Investigate discrepancy between frontend totals.total and backend totalCents.",
+      "priority": "high",
+      "risk": "med",
+      "status": "in_progress",
+      "created_at": "2026-08-26",
+      "gates": {
+        "reviewer": false,
+        "security": false,
+        "qa": false
+      },
+      "phase": "pos"
     }
   ]
 }