events: Phase 1 calendar — DAILY/WEEKLY RRULE expansion + 24 tests

Civil date arithmetic (Hinnant), integer epoch-minute datetimes, bounded
windowed RRULE expansion (DAILY/WEEKLY with INTERVAL/COUNT/UNTIL/BYDAY),
multi-event merge. Conformance harness + scoreboard wired.

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

lib/events/conformance.conf

@@ -0,0 +1,23 @@
+# events-on-sx conformance config — sourced by lib/guest/conformance.sh.
+
+LANG_NAME=events
+MODE=dict
+SCOREBOARD_DIR=lib/events
+
+PRELOADS=(
+  lib/datalog/tokenizer.sx
+  lib/datalog/parser.sx
+  lib/datalog/unify.sx
+  lib/datalog/db.sx
+  lib/datalog/builtins.sx
+  lib/datalog/aggregates.sx
+  lib/datalog/strata.sx
+  lib/datalog/eval.sx
+  lib/datalog/api.sx
+  lib/datalog/magic.sx
+  lib/events/calendar.sx
+)
+
+SUITES=(
+  "calendar:lib/events/tests/calendar.sx:(ev-calendar-tests-run!)"
+)