feat: add SQLite and PostgreSQL event queue adapters with migrations

.env.example

@@ -38,12 +38,22 @@ SECURE_COOKIES=false
 ALLOW_REGISTRATION=false
 RATE_LIMIT=20
 POSTER_FETCH_TIMEOUT_SECONDS=30
-EVENT_CHANNEL_BUFFER=128
 
-# NATS event bus (optional — falls back to in-memory channel when unset)
+# Event bus — controls background poster sync and other async work.
+# Priority: NATS (if NATS_URL set) → DB queue (default, uses existing DB)
+# The worker binary must run alongside the presentation to process events.
+
+# Option A: DB queue (default — no extra infrastructure needed)
+# Events are stored in the same database as the app and polled by the worker.
+# EVENT_QUEUE_POLL_INTERVAL_MS=500   # polling interval (default: 500ms)
+# EVENT_QUEUE_BATCH_SIZE=10          # rows claimed per poll cycle (default: 10)
+# EVENT_QUEUE_MAX_ATTEMPTS=5         # retries before dead-lettering (default: 5)
+
+# Option B: NATS (at-least-once delivery, recommended for higher throughput)
 # NATS_URL=nats://localhost:4222
 # NATS_MODE=jetstream           # "jetstream" (default, at-least-once) or "core" (fire-and-forget)
 # NATS_SUBJECT_PREFIX=movies-diary.events
 # NATS_STREAM_NAME=MOVIES_DIARY_EVENTS
 # NATS_CONSUMER_NAME=worker
-RUST_LOG=presentation=debug,tower_http=debug
+
+RUST_LOG=presentation=debug,tower_http=debug,worker=info,application=info