Fixes time zone based stuff

src/lib/components/DateTimePicker.svelte

@@ -29,7 +29,9 @@
 
   const seed = untrack(() => {
     if (initialValue) {
-      const d = new Date(initialValue)
+      // Append Z if no timezone indicator is present so it's always parsed as UTC
+      const normalized = /Z$|[+-]\d{2}:?\d{2}$/.test(initialValue) ? initialValue : initialValue + 'Z'
+      const d = new Date(normalized)
       return { month: d.getMonth(), day: d.getDate(), year: d.getFullYear(), timeIndex: d.getHours() * 4 + Math.round(d.getMinutes() / 15) }
     }
     const today = new Date()
@@ -48,10 +50,9 @@
   })
 
   $effect(() => {
-    const pad = (n: number) => n.toString().padStart(2, '0')
     const hour = Math.floor(timeIndex / 4)
     const minute = (timeIndex % 4) * 15
-    value = new Date(`${year}-${pad(month + 1)}-${pad(day)}T${pad(hour)}:${pad(minute)}`).toISOString()
+    value = new Date(year, month, day, hour, minute).toISOString()
   })
 </script>