Buchungskalender: iCal-Import und -Export

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/fixtures/ical/tzid.ics

@@ -0,0 +1,39 @@
+BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//Test//EN
+BEGIN:VEVENT
+UID:z1
+DTSTART:20261110T140000Z
+DTEND:20261112T100000Z
+END:VEVENT
+BEGIN:VEVENT
+UID:z2
+DTSTART;TZID=Europe/Berlin:20261110T000000
+DTEND;TZID=Europe/Berlin:20261112T000000
+END:VEVENT
+BEGIN:VEVENT
+UID:z3
+DTSTART:20261130T233000Z
+DTEND:20261202T100000Z
+END:VEVENT
+BEGIN:VEVENT
+UID:z4
+DTSTART;VALUE=DATE:20261215
+END:VEVENT
+BEGIN:VEVENT
+UID:z5
+DTSTART;VALUE=DATE:20261220
+DTEND;VALUE=DATE:20261222
+STATUS:CANCELLED
+END:VEVENT
+BEGIN:VEVENT
+UID:z6
+DTSTART;VALUE=DATE:20200101
+DTEND;VALUE=DATE:20200105
+END:VEVENT
+BEGIN:VEVENT
+UID:z7
+DTSTART;VALUE=DATE:20300101
+DTEND;VALUE=DATE:20300105
+END:VEVENT
+END:VCALENDAR