events: iCalendar import + occurrence-exact round-trip + 19 tests

ical.sx parses VEVENT/VCALENDAR text back into events (ev/ical-lines->event,
ev/parse-vcalendar): DTSTART/DURATION/RRULE (ordinal BYDAY, BYMONTHDAY, UNTIL/
COUNT/INTERVAL) + EXDATE/RDATE. Round-trip is occurrence-exact — export->import
expands to the identical occurrence set. Completes bidirectional interop.
360/360 green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/events/scoreboard.json

@@ -1,12 +1,12 @@
 {
   "lang": "events",
-  "total_passed": 341,
+  "total_passed": 360,
   "total_failed": 0,
-  "total": 341,
+  "total": 360,
   "suites": [
     {"name":"calendar","passed":51,"failed":0,"total":51},
     {"name":"timezone","passed":17,"failed":0,"total":17},
-    {"name":"ical","passed":21,"failed":0,"total":21},
+    {"name":"ical","passed":40,"failed":0,"total":40},
     {"name":"availability","passed":22,"failed":0,"total":22},
     {"name":"api","passed":41,"failed":0,"total":41},
     {"name":"booking","passed":82,"failed":0,"total":82},
@@ -17,5 +17,5 @@
     {"name":"federation","passed":29,"failed":0,"total":29},
     {"name":"integration","passed":8,"failed":0,"total":8}
   ],
-  "generated": "2026-06-07T15:20:08+00:00"
+  "generated": "2026-06-07T17:28:07+00:00"
 }