Fix of some timezone problems

Web/app.py

@@ -7990,8 +7990,12 @@ def check_availability():
         items_col = db['items']
 
         # Collect potential conflicts (planned and active) for this day
-        same_day_start = datetime.datetime.combine(booking_date.date(), datetime.time.min)
-        same_day_end = datetime.datetime.combine(booking_date.date(), datetime.time.max)
+        same_day_start = datetime.datetime.combine(
+            booking_date.date(), datetime.time.min, tzinfo=ZoneInfo("Europe/Berlin")
+        )
+        same_day_end = datetime.datetime.combine(
+            booking_date.date(), datetime.time.max, tzinfo=ZoneInfo("Europe/Berlin")
+        )
         candidates = list(ausleihungen.find({
             'Item': item_id,
             'Status': {'$in': ['planned', 'active']},
@@ -8009,6 +8013,8 @@ def check_availability():
             if r_start is None:
                 r_start = same_day_start
             # Overlap check: req_start < r_end and req_end > r_start
+            r_start = au.ensure_timezone_aware(r_start)
+            r_end = au.ensure_timezone_aware(r_end)
             if req_start < r_end and req_end > r_start:
                 conflicts.append({
                     'id': str(r.get('_id')),
@@ -8223,16 +8229,19 @@ def add_booking():
     period = request.form.get('period')
     notes = request.form.get('notes', '')
     
-    # Parse dates as naive datetime objects
+    # Form timestamps represent local school time.
     try:
-        # Simple datetime parsing without timezone
         if start_date_str:
-            start_date = datetime.datetime.strptime(start_date_str, '%Y-%m-%d %H:%M:%S')
+            start_date = datetime.datetime.strptime(
+                start_date_str, '%Y-%m-%d %H:%M:%S'
+            ).replace(tzinfo=ZoneInfo("Europe/Berlin"))
         else:
             return jsonify({'success': False, 'error': 'Missing start date'})
         
         if end_date_str:
-            end_date = datetime.datetime.strptime(end_date_str, '%Y-%m-%d %H:%M:%S')
+            end_date = datetime.datetime.strptime(
+                end_date_str, '%Y-%m-%d %H:%M:%S'
+            ).replace(tzinfo=ZoneInfo("Europe/Berlin"))
         else:
             end_date = None
         
@@ -11274,12 +11283,14 @@ def get_period_times(booking_date, period_num):
         # Create datetime objects for start and end times
         start_datetime = datetime.datetime.combine(
             booking_date.date(),
-            datetime.time(start_hour, start_min)
+            datetime.time(start_hour, start_min),
+            tzinfo=ZoneInfo("Europe/Berlin")
         )
         
         end_datetime = datetime.datetime.combine(
             booking_date.date(),
-            datetime.time(end_hour, end_min)
+            datetime.time(end_hour, end_min),
+            tzinfo=ZoneInfo("Europe/Berlin")
         )
         
         return {