feat: sync all-day events for shifts without time (Frei, holidays, etc.)

Both Google Calendar and Nextcloud CalDAV now create all-day events for
shifts that have no MorningTime or AfternoonTime configured, instead of
silently skipping them. Fixes month-boundary crash on day 31 by using
DateOnly.AddDays(1) for the end date.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Services/GoogleCalendarService.cs

@@ -84,7 +84,12 @@ public class GoogleCalendarService(IHttpContextAccessor httpContextAccessor, ICo
         var date = shiftWithTransport.Date;
 
         if (string.IsNullOrEmpty(shift.MorningTime) && string.IsNullOrEmpty(shift.AfternoonTime))
+        {
+            var eventData = CalendarEventBuilder.BuildEventContent(shift, null);
+            var allDayEvent = CreateAllDayGoogleEvent(eventData, DateOnly.FromDateTime(date));
+            await CalendarEventBuilder.ExecuteWithRetryAsync(async () => await service.Events.Insert(allDayEvent, calendarId).ExecuteAsync());
             return;
+        }
 
         if (!string.IsNullOrEmpty(shift.MorningTime))
         {
@@ -103,6 +108,26 @@ public class GoogleCalendarService(IHttpContextAccessor httpContextAccessor, ICo
         }
     }
 
+    private static Event CreateAllDayGoogleEvent(CalendarEventData eventData, DateOnly date)
+    {
+        var dateStr = date.ToString("yyyy-MM-dd");
+        var nextDateStr = date.AddDays(1).ToString("yyyy-MM-dd");
+        return new Event
+        {
+            Summary = eventData.Summary,
+            Start = new EventDateTime { Date = dateStr },
+            End = new EventDateTime { Date = nextDateStr },
+            ExtendedProperties = new Event.ExtendedPropertiesData
+            {
+                Private__ = new Dictionary<string, string>
+                {
+                    ["shiftSchedulerEvent"] = "true",
+                    ["shiftName"] = eventData.Summary
+                }
+            }
+        };
+    }
+
     private static Event CreateGoogleEvent(CalendarEventData eventData, DateTimeOffset startTime, DateTimeOffset endTime)
     {
         return new Event

Services/NextcloudCalendarService.cs

@@ -162,7 +162,16 @@ public class NextcloudCalendarService(
             var date = shiftWithTransport.Date;
 
             if (string.IsNullOrEmpty(shift.MorningTime) && string.IsNullOrEmpty(shift.AfternoonTime))
+            {
+                var uid = $"shift-{SanitizeForUid(shift.Name)}-{date:yyyyMMdd}-allday";
+                var eventData = CalendarEventBuilder.BuildEventContent(shift, null);
+                var icsContent = BuildAllDayIcsContent(uid, eventData, DateOnly.FromDateTime(date));
+                var putRequest = CreateRequest(HttpMethod.Put, $"{calendarId}{Uri.EscapeDataString(uid)}.ics");
+                putRequest.Content = new StringContent(icsContent, Encoding.UTF8, "text/calendar");
+                (await client.SendAsync(putRequest)).EnsureSuccessStatusCode();
+                await Task.Delay(300);
                 continue;
+            }
 
             if (!string.IsNullOrEmpty(shift.MorningTime))
             {
@@ -194,6 +203,21 @@ public class NextcloudCalendarService(
         }
     }
 
+    private static string BuildAllDayIcsContent(string uid, CalendarEventData eventData, DateOnly date)
+    {
+        var calendar = new Calendar();
+        var vevent = new CalendarEvent
+        {
+            Uid = uid,
+            Summary = eventData.Summary,
+            DtStart = new CalDateTime(date.Year, date.Month, date.Day),
+            DtEnd = new CalDateTime(date.AddDays(1).Year, date.AddDays(1).Month, date.AddDays(1).Day)
+        };
+        vevent.Properties.Add(new Ical.Net.CalendarProperty("X-SHIFT-SCHEDULER", "TRUE"));
+        calendar.Events.Add(vevent);
+        return new CalendarSerializer().SerializeToString(calendar)!;
+    }
+
     private static string BuildIcsContent(string uid, CalendarEventData eventData, DateTimeOffset startTime, DateTimeOffset endTime)
     {
         var calendar = new Calendar();