fix: recalculate navigation offset after URL date restore

Arrow navigation was relative to current period instead of the
restored range. Now recomputes monthOffset from the difference
between restored dates and current period on URL restore.

app/javascript/dashboard/components/ui/DatePicker/DatePicker.vue

@@ -20,6 +20,7 @@ import {
   addMonths,
   isSameMonth,
   differenceInCalendarMonths,
+  differenceInCalendarWeeks,
   setMonth,
   setYear,
   getWeek,
@@ -141,6 +142,26 @@ watch(
       endCurrentDate.value = isSameMonth(newDateRange[0], newDateRange[1])
         ? startOfMonth(addMonths(newDateRange[1], 1))
         : startOfMonth(newDateRange[1]);
+
+      // Recalculate offset so arrow navigation is relative to restored range
+      if (isNavigableRange(selectedRange.value)) {
+        const current = getActiveDateRange(
+          selectedRange.value,
+          currentDate.value
+        );
+        if (selectedRange.value === DATE_RANGE_TYPES.THIS_WEEK) {
+          monthOffset.value = differenceInCalendarWeeks(
+            newDateRange[0],
+            current.start,
+            { weekStartsOn: 1 }
+          );
+        } else {
+          monthOffset.value = differenceInCalendarMonths(
+            newDateRange[0],
+            current.start
+          );
+        }
+      }
     }
   },
   { immediate: true }