events: iCalendar (RFC 5545) export + 21 tests

ical.sx serializes events to VEVENT/VCALENDAR text for import by standard
clients: UTC basic-format stamps, DURATION (PT#H#M), full RRULE
(FREQ/INTERVAL/COUNT/UNTIL/BYDAY incl. monthly ordinals 2TU/-1FR/BYMONTHDAY)
plus EXDATE/RDATE. Line-oriented (ev/event->ical-lines / ev/events->ical-lines)
with ev/ical-render joining CRLF for the wire format. 332/332 green.

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

lib/events/scoreboard.json

@@ -1,11 +1,12 @@
 {
   "lang": "events",
-  "total_passed": 311,
+  "total_passed": 332,
   "total_failed": 0,
-  "total": 311,
+  "total": 332,
   "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":"availability","passed":22,"failed":0,"total":22},
     {"name":"api","passed":32,"failed":0,"total":32},
     {"name":"booking","passed":82,"failed":0,"total":82},
@@ -16,5 +17,5 @@
     {"name":"federation","passed":29,"failed":0,"total":29},
     {"name":"integration","passed":8,"failed":0,"total":8}
   ],
-  "generated": "2026-06-07T13:59:09+00:00"
+  "generated": "2026-06-07T14:40:54+00:00"
 }