events: api.sx — public events facade + 14 tests (Phase 1 complete)

Immutable store ({:events :bookings}) over calendar+availability:
ev/schedule, ev/book, ev/agenda, ev/agenda-for, ev/free?, ev/next-free,
ev/conflicts. Availability queries auto-widen expansion by longest event.
73/73 green. Phase 1 done.

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

lib/events/scoreboard.json

@@ -1,11 +1,12 @@
 {
   "lang": "events",
-  "total_passed": 59,
+  "total_passed": 73,
   "total_failed": 0,
-  "total": 59,
+  "total": 73,
   "suites": [
     {"name":"calendar","passed":37,"failed":0,"total":37},
-    {"name":"availability","passed":22,"failed":0,"total":22}
+    {"name":"availability","passed":22,"failed":0,"total":22},
+    {"name":"api","passed":14,"failed":0,"total":14}
   ],
-  "generated": "2026-06-07T00:49:23+00:00"
+  "generated": "2026-06-07T01:15:49+00:00"
 }