Fixed the date shift by making date-only strings stay in the user timezone instead of being converted from UTC, which caused the one-day rollback.

app/Services/TimeService.php

@@ -167,8 +167,13 @@ class TimeService
             return null;
         }
 
-        $sourceTz = $sourceTz ?: $this->serverTimezone;
         $targetTz = $targetTz ?: $this->userTimezone();
+        if ($sourceTz === null && $this->isDateOnlyString($value)) {
+            // Date-only strings should not shift across timezones.
+            $sourceTz = $targetTz;
+        } else {
+            $sourceTz = $sourceTz ?: $this->serverTimezone;
+        }
 
         try {
             if ($value instanceof Time) {
@@ -204,4 +209,14 @@ class TimeService
     {
         return (string) ($this->toUTC($value, $fromTz, $format) ?? '');
     }
+
+    private function isDateOnlyString($value): bool
+    {
+        if (!is_string($value)) {
+            return false;
+        }
+
+        $value = trim($value);
+        return (bool) preg_match('/^\d{4}-\d{2}-\d{2}$/', $value);
+    }
 }