events: availability.sx — free/busy + conflict detection on Datalog + 16 tests

occurrence/booking EDB; rules busy/conflict (canonical pair, half-open
overlap)/busy_in. API ev-busy, ev-conflicts, ev-has-conflict?, ev-free?
(transient qwindow). Integrates with calendar expansion. 53/53 green.

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

lib/events/scoreboard.json

@@ -1,10 +1,11 @@
 {
   "lang": "events",
-  "total_passed": 37,
+  "total_passed": 53,
   "total_failed": 0,
-  "total": 37,
+  "total": 53,
   "suites": [
-    {"name":"calendar","passed":37,"failed":0,"total":37}
+    {"name":"calendar","passed":37,"failed":0,"total":37},
+    {"name":"availability","passed":16,"failed":0,"total":16}
   ],
-  "generated": "2026-06-06T23:52:14+00:00"
+  "generated": "2026-06-07T00:21:06+00:00"
 }