Dual device on weekend feature

frontend/src/components/Calendar.jsx

@@ -53,6 +53,8 @@ export default function Calendar({
   daytimeDateKey = null,
   weekStart,
   onWeekChange,
+  dualDeviceWeekendWeekEnabled = false,
+  onDualDeviceWeekendWeekEnabledChange,
   windowLookup = new Map(),
   onWindowSelect,
 }) {
@@ -111,6 +113,25 @@ export default function Calendar({
         >
           Today
         </button>
+        <div className="ml-auto flex items-center gap-2 text-xs text-gray-300 select-none">
+          <span>Run both devices on weekend this week</span>
+          <button
+            type="button"
+            role="switch"
+            aria-checked={dualDeviceWeekendWeekEnabled}
+            onClick={() => onDualDeviceWeekendWeekEnabledChange?.(!dualDeviceWeekendWeekEnabled)}
+            className={`relative inline-flex h-5 w-9 shrink-0 cursor-pointer rounded-full border-2 border-transparent transition-colors focus:outline-none focus:ring-2 focus:ring-blue-500/70 ${
+              dualDeviceWeekendWeekEnabled ? 'bg-blue-600' : 'bg-gray-600'
+            }`}
+            title="Toggle dual-device weekend-start scheduling for this week"
+          >
+            <span
+              className={`pointer-events-none inline-block h-4 w-4 rounded-full bg-white shadow transform transition-transform ${
+                dualDeviceWeekendWeekEnabled ? 'translate-x-4' : 'translate-x-0'
+              }`}
+            />
+          </button>
+        </div>
       </div>
 
       {/* 7-day grid */}