fix dual device and calendar display bug

frontend/src/components/DayColumn.jsx

@@ -18,11 +18,16 @@ export default function DayColumn({
   const dayName = DAY_NAMES[date.getDay()]
   const dayNum  = date.getDate()
   const dateKey = date.toISOString().slice(0, 10)
+  const nextDateKey = new Date(date.getTime() + (24 * 60 * 60 * 1000)).toISOString().slice(0, 10)
 
   function getWindowForShift(shiftIndex) {
     return windowLookup.get(`${dateKey}::shift${shiftIndex}`) ?? null
   }
 
+  function getNextDayShift1Window() {
+    return windowLookup.get(`${nextDateKey}::shift1`) ?? null
+  }
+
   const shift2Visible = showShift2 || shifts.shift2.length > 0 || Boolean(getWindowForShift(2))
 
   return (
@@ -65,7 +70,7 @@ export default function DayColumn({
           tests={nextDayShift1}
           visible={true}
           active={nextDayShift1Active}
-          windowDetails={null}
+          windowDetails={getNextDayShift1Window()}
           minContentRows={shiftMinRows.nextDayShift1}
           slotHeightPx={slotHeights.nextDayShift1}
           onWindowSelect={onWindowSelect}

frontend/src/components/SettingsModal.jsx

@@ -259,9 +259,9 @@ export default function SettingsModal({ isOpen, onClose, settings, onSave }) {
               Holidays
             </p>
             <Field label="Holiday Dates" hint="(comma-separated, YYYY-MM-DD)">
-              <input
-                type="text"
+              <textarea
                 className={INPUT_CLS}
+                rows={4}
                 placeholder="2026-07-04, 2026-12-25…"
                 value={form.holidays ?? ''}
                 onChange={(e) => set('holidays', e.target.value)}

frontend/src/components/ShiftSlot.jsx

@@ -42,7 +42,12 @@ export default function ShiftSlot({
         style={{ minHeight: `${minContentHeightPx}px` }}
       >
         {tests.length === 0 ? null : (
-          tests.map((test) => <TestCard key={`${test.test_id}-${test.device}`} test={test} />)
+          tests.map((test, index) => (
+            <TestCard
+              key={`${test.test_id}-${test.device}-${test.scheduled_date ?? 'na'}-${test.shift_index ?? 'na'}-${test.sequence_in_shift ?? index}`}
+              test={test}
+            />
+          ))
         )}
       </div>
     </div>

frontend/src/components/TestWindowDetailsPanel.jsx

@@ -183,6 +183,10 @@ function TestRow({ test }) {
 
 export default function TestWindowDetailsPanel({ isOpen, windowDetails, onClose }) {
   const [showConfigMap, setShowConfigMap] = useState(false)
+  const windowTests = useMemo(
+    () => (Array.isArray(windowDetails?.tests) ? windowDetails.tests : []),
+    [windowDetails],
+  )
   const windowTestConfig = useMemo(() => getWindowTestConfig(windowDetails), [windowDetails])
   const windowConfigMapKey = useMemo(
     () => (windowTestConfig.length > 0 ? String(windowTestConfig[0]).toUpperCase() : null),
@@ -311,12 +315,15 @@ export default function TestWindowDetailsPanel({ isOpen, windowDetails, onClose
                 <div className="mt-5">
                   <div className="flex items-center justify-between gap-3 mb-3">
                     <p className="text-sm font-semibold text-white">Tests Scheduled In This Window</p>
-                    <span className="text-xs text-gray-500">{windowDetails.tests?.length ?? 0} tests</span>
+                    <span className="text-xs text-gray-500">{windowTests.length} tests</span>
                   </div>
-                  {windowDetails.tests?.length ? (
+                  {windowTests.length ? (
                     <div className="flex flex-col gap-3">
-                      {windowDetails.tests.map((test) => (
-                        <TestRow key={`${test.test_id}-${test.device}-${test.scheduled_date}-${test.shift_index}`} test={test} />
+                      {windowTests.map((test, index) => (
+                        <TestRow
+                          key={`${test.test_id}-${test.device}-${test.scheduled_date ?? 'na'}-${test.shift_index ?? 'na'}-${test.sequence_in_shift ?? index}`}
+                          test={test}
+                        />
                       ))}
                     </div>
                   ) : (