test: cover NATS bridge + Todoist scheduler; ADR-0010

- bus.test.ts: 4 cases for the new onPublish hook contract
- nats.test.ts: stream creation idempotency + JSON publish bridge
- scheduler.test.ts: startup delay, fan-out, per-user failure isolation
- ADR-0010 documents the bridge-don't-replace decision and the
  Todoist scheduler isolation, plus open follow-ups (#98 ml/serving
  consumer, #54 protobuf migration, graceful shutdown, metrics)
- README/overview/services README reflect the bridged event substrate
- CLAUDE.md gains a "don't nats.publish() directly" rule
- .env.example documents NATS_URL + TODOIST_SYNC_INTERVAL_MS

Verified in deployment 2026-04-18: api -> nats bridge connects on
boot, signals + feedback streams created, scheduler tick logs
"todoist sync: 1 ok, 0 failed (1 users)" within 10s. Closes #21, #22.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.env.example

@@ -27,3 +27,11 @@ VAPID_SUBJECT=mailto:you@example.com
 # Todoist OAuth — https://developer.todoist.com/appconsole.html
 TODOIST_CLIENT_ID=
 TODOIST_CLIENT_SECRET=
+
+# Event bus — leave NATS_URL empty for in-process bus only (no JetStream bridge).
+# Set to nats://nats:4222 (compose service name) or nats://localhost:4222 (host)
+# to mirror every publish to durable JetStream streams (signals.>, feedback.>).
+# Start the broker with: docker compose --profile events up nats
+NATS_URL=
+# How often the background scheduler refreshes Todoist tasks per active user (ms).
+TODOIST_SYNC_INTERVAL_MS=900000