events: RRULE EXDATE/RDATE exceptions + 8 tests

ev-event-full carries :exdate/:rdate. ev-expand-base = raw expansion;
ev-expand applies exceptions: RDATE adds in-window occurrences, EXDATE removes
matching starts, de-duped, EXDATE wins over RDATE and the rrule (RFC 5545).
RDATE-only events supported; plain ev-event unaffected. 248/248 green.

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

lib/events/scoreboard.json

@@ -1,10 +1,10 @@
 {
   "lang": "events",
-  "total_passed": 240,
+  "total_passed": 248,
   "total_failed": 0,
-  "total": 240,
+  "total": 248,
   "suites": [
-    {"name":"calendar","passed":37,"failed":0,"total":37},
+    {"name":"calendar","passed":45,"failed":0,"total":45},
     {"name":"availability","passed":22,"failed":0,"total":22},
     {"name":"api","passed":24,"failed":0,"total":24},
     {"name":"booking","passed":82,"failed":0,"total":82},
@@ -13,5 +13,5 @@
     {"name":"reminders","passed":14,"failed":0,"total":14},
     {"name":"federation","passed":23,"failed":0,"total":23}
   ],
-  "generated": "2026-06-07T05:59:03+00:00"
+  "generated": "2026-06-07T06:25:58+00:00"
 }