refactor: fix bugs in calendar logic across duration parsing, RFC compliance, and event handling

- Fix buildDuration() trailing "T" producing invalid ISO 8601 durations
- Fix DURATION_RE missing week (W) support in alerts and invitation parsing
- Fix computeFireTime() end fallback when utcEnd is missing
- Fix recurrenceOverrides patch escaping per RFC 6901 (updateEvent/rsvpEvent)
- Fix layoutOverlappingEvents endMin overflow past 1440
- Fix addDurationToDate() to support weeks and use UTC methods for UTC inputs
- Fix getEffectiveAlerts() null guard on calendarIds
- Fix buildAllDayDuration() DST-safe day calculation using differenceInCalendarDays
- Fix participant matching to check calendarAddress and sendTo (not just email)
- Fix buildParticipantMap() using crypto.randomUUID() instead of hardcoded IDs
- Fix overnight preview negative endMin in week view
- Fix sendImipInvitation() to emit DURATION when utcEnd is absent
- Fix sendImipCancellation() to validate status before sending
- Fix createEvent() to remap all calendarIds for shared calendars
- Fix getCalendarTasks() to clone before mutating @type
- Fix importEvents() error matching to include 'duplicate' and 'conflict'
- Fix looksLikeReply() false positive by requiring organizer + responded attendee
- Fix alert offset regex to require T before minutes
- Fix handleDuplicate() to generate new UID
- Fix formatSnapTime() input clamping
- Replace console.log/error with debug.log/error/warn in iMIP functions

components/calendar/calendar-week-view.tsx

@@ -448,7 +448,8 @@ export function CalendarWeekView({
                   {pendingPreview && !pendingPreview.allDay && isSameDay(pendingPreview.start, day) && (
                     (() => {
                       const startMin = pendingPreview.start.getHours() * 60 + pendingPreview.start.getMinutes();
-                      const endMin = pendingPreview.end.getHours() * 60 + pendingPreview.end.getMinutes();
+                      let endMin = pendingPreview.end.getHours() * 60 + pendingPreview.end.getMinutes();
+                      if (endMin <= startMin) endMin = 1440;
                       const durationMin = Math.max(15, endMin - startMin);
                       const cal = calendars.find(c => c.id === pendingPreview.calendarId);
                       const color = cal?.color || "hsl(var(--primary))";