fix: normalize task datetimes before travel expense min/max

Prevent 500 errors on travel-expenses-table when work-hour entries mix
naive and timezone-aware datetimes. Normalize all candidate datetimes to
a consistent timezone before min/max comparisons.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

backend/modules/fleet/views.py

@@ -304,6 +304,14 @@ def _format_decimal_fixed(value, *, default='0.00', places=2):
     return format(normalized.quantize(quantizer), 'f')
 
 
+def _normalize_datetime_for_compare(value):
+    if not isinstance(value, datetime):
+        return value
+    if timezone.is_naive(value):
+        return timezone.make_aware(value, timezone.get_current_timezone())
+    return timezone.localtime(value)
+
+
 def _work_order_travel_expenses_context(work_order):
     related_tasks = list(_work_order_related_tasks_queryset(work_order))
     trip_entries = []
@@ -318,8 +326,16 @@ def _work_order_travel_expenses_context(work_order):
 
     if trip_entries:
         entry_dates = [entry['date'] for entry in trip_entries if entry.get('date')]
-        start_candidates = [entry['start_dt'] for entry in trip_entries if entry.get('start_dt')]
-        end_candidates = [entry['end_dt'] for entry in trip_entries if entry.get('end_dt')]
+        start_candidates = [
+            _normalize_datetime_for_compare(entry.get('start_dt'))
+            for entry in trip_entries
+            if entry.get('start_dt')
+        ]
+        end_candidates = [
+            _normalize_datetime_for_compare(entry.get('end_dt'))
+            for entry in trip_entries
+            if entry.get('end_dt')
+        ]
         if entry_dates:
             trip_start_date = min(entry_dates)
             trip_end_date = max(entry_dates)