events: VTIMEZONE iCal export — full DST-correct tz recurrence + 16 tests

A tz event now exports DTSTART;TZID=<name>:<local> (EXDATE/RDATE likewise;
UNTIL stays UTC per RFC), and the VCALENDAR emits a VTIMEZONE per distinct zone
with DAYLIGHT/STANDARD sub-components generated from the zone's transition rules
(offsets + FREQ=YEARLY;BYMONTH;BYDAY) — London/Paris blocks match real-world
definitions. Clients recur at fixed wall-clock time, DST-correct (prior caveat
gone). Importer tolerates ;TZID= params. 376/376 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": 366,
+  "total_passed": 376,
   "total_failed": 0,
-  "total": 366,
+  "total": 376,
   "suites": [
     {"name":"calendar","passed":51,"failed":0,"total":51},
     {"name":"timezone","passed":17,"failed":0,"total":17},
-    {"name":"ical","passed":46,"failed":0,"total":46},
+    {"name":"ical","passed":56,"failed":0,"total":56},
     {"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": "2026-06-07T18:33:58+00:00"
+  "generated": "2026-06-07T20:02:48+00:00"
 }