Fix time slot picker bugs for past dates

Fixed issues:
- Added isAvailable parameter to handleSlotClick to prevent clicks on unavailable slots
- Added validation to prevent selecting past dates in date picker
- Added validation in handlePreviousDay to block navigating to past dates
- Added warning message when trying to view past dates
- Prevents the "slot is not defined" error when clicking disabled slots

Now the modal properly:
- Blocks selecting dates before today
- Shows clear error messages for past dates
- Prevents clicks on unavailable time slots
- Handles edge cases like passed sessions being rescheduled

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/components/admin/TimeSlotPickerModal.tsx

@@ -120,6 +120,10 @@ export function TimeSlotPickerModal({
   // Date navigation handlers
   const handlePreviousDay = () => {
     const newDate = addDays(currentDate, -1);
+    // Prevent going to past dates
+    if (isPast(newDate) && !isToday(newDate)) {
+      return;
+    }
     setCurrentDate(newDate);
   };
 
@@ -131,6 +135,10 @@ export function TimeSlotPickerModal({
   const handleDateChange = (e: React.ChangeEvent<HTMLInputElement>) => {
     const newDate = parse(e.target.value, 'yyyy-MM-dd', new Date());
     if (!isNaN(newDate.getTime())) {
+      // Prevent selecting past dates
+      if (isPast(newDate) && !isToday(newDate)) {
+        return;
+      }
       setCurrentDate(newDate);
     }
   };
@@ -208,8 +216,9 @@ export function TimeSlotPickerModal({
   const totalBlocks = getSlotsInRange().length;
   const totalDuration = totalBlocks * (settings?.consulting_block_duration_minutes || 30);
 
-  const handleSlotClick = (slotStart: string) => {
+  const handleSlotClick = (slotStart: string, isAvailable: boolean) => {
-    if (!slot.available) return;
+    // Prevent clicking on unavailable slots
+    if (!isAvailable) return;
 
     // No selection yet → Set as pending
     if (!selectedRange.start) {
@@ -327,7 +336,13 @@ export function TimeSlotPickerModal({
               </div>
 
               {/* Info */}
-              {isToday(currentDate) && timeSlots.length === 0 ? (
+              {isPast(currentDate) && !isToday(currentDate) ? (
+                <div className="bg-destructive/10 border-2 border-destructive/20 p-4 rounded-lg text-center">
+                  <p className="text-sm text-destructive font-medium">
+                    Tidak dapat memilih tanggal yang sudah lewat. Silakan pilih tanggal hari ini atau tanggal yang akan datang.
+                  </p>
+                </div>
+              ) : isToday(currentDate) && timeSlots.length === 0 ? (
                 <div className="bg-amber-50 dark:bg-amber-950 border-2 border-amber-200 dark:border-amber-800 p-4 rounded-lg text-center">
                   <p className="text-sm text-amber-900 dark:text-amber-100">
                     Tidak ada slot tersedia untuk sisa hari ini. Silakan pilih tanggal lain.
@@ -367,7 +382,7 @@ export function TimeSlotPickerModal({
                             !slot.available ? 'opacity-30 cursor-not-allowed' : ''
                           }`}
                           disabled={!slot.available}
-                          onClick={() => handleSlotClick(slot.start)}
+                          onClick={() => handleSlotClick(slot.start, slot.available)}
                         >
                           {slot.start}
                         </Button>