events: end-to-end delivery pipeline (derivation -> notify flow) + 8 tests

ev/deliver-messages bridges SX notification messages to the Scheme notify
flow: each (id recipient body) is serialized to s-expr text, spliced as quoted
data into the digest-flow program, delivered over an injected transport, and
results unboxed. Integration suite drives all three derivations (reminders /
booking-notify / reschedule) through delivery end to end; empty batch guarded
(empty digest completes without suspending). 303/303 green.

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

lib/events/conformance.conf

@@ -57,4 +57,5 @@ SUITES=(
   "notify:lib/events/tests/notify.sx:(ev-notify-tests-run!)"
   "reminders:lib/events/tests/reminders.sx:(ev-reminders-tests-run!)"
   "federation:lib/events/tests/federation.sx:(ev-federation-tests-run!)"
+  "integration:lib/events/tests/integration.sx:(ev-integration-tests-run!)"
 )