replace tokio::broadcast event bus with SQLite-backed event queue (ADR-0003)

- DomainEvent: add Serialize/Deserialize
- EventConsumer port: poll_next/ack/nack replacing recv()
- EventEnvelope: wraps event with id/retry_count/created_at
- SqliteEventPublisher/SqliteEventConsumer: INSERT/poll/DLQ
- migration: event_queue + dead_letter_queue tables
- InMemoryEventBus: combined publisher+consumer test double
- NoopEventConsumer: test stub
- webhook_consumer: polls EventConsumer instead of broadcast::Receiver
- presentation+mcp wiring: create from SqlitePool

crates/presentation/src/factory.rs

@@ -17,7 +17,6 @@ use infra_wiring::{Config, ConfigSource, DbPool};
 
 use crate::state::AppState;
 
-const EVENT_BUS_CAPACITY: usize = 64;
 const DEV_JWT_SECRET: &str = "k-template-dev-secret-not-for-production-use-only";
 
 pub async fn build_app_state(config: Config) -> anyhow::Result<AppState> {
@@ -29,8 +28,14 @@ pub async fn build_app_state(config: Config) -> anyhow::Result<AppState> {
     let auth_service: Arc<dyn domain::ports::AuthService> =
         Arc::new(adapter_auth::PasswordAuthService);
 
-    let event_bus = Arc::new(adapter_event_publisher::ChannelEventBus::new(EVENT_BUS_CAPACITY));
-    let event_publisher: Arc<dyn domain::ports::EventPublisher> = event_bus.clone();
+    let sqlite_pool = match &pool {
+        #[cfg(feature = "sqlite")]
+        DbPool::Sqlite(p) => p.clone(),
+    };
+    let event_publisher: Arc<dyn domain::ports::EventPublisher> =
+        Arc::new(adapter_event_publisher::SqliteEventPublisher::new(sqlite_pool.clone()));
+    let event_consumer: Arc<dyn domain::ports::EventConsumer> =
+        Arc::new(adapter_event_publisher::SqliteEventConsumer::new(sqlite_pool));
 
     let provider_registry = build_provider_registry(&config).await;
 
@@ -134,10 +139,10 @@ pub async fn build_app_state(config: Config) -> anyhow::Result<AppState> {
         bg_event_publisher,
     ));
 
-    let webhook_rx = event_bus.subscriber();
+    let webhook_consumer = event_consumer.clone();
     let webhook_channel_query = wire_output.channel_query.clone();
     tokio::spawn(crate::background::webhook_consumer::run(
-        webhook_rx,
+        webhook_consumer,
         webhook_channel_query,
         reqwest::Client::new(),
     ));
@@ -172,7 +177,8 @@ pub async fn build_app_state(config: Config) -> anyhow::Result<AppState> {
         #[cfg(feature = "auth-jwt")]
         jwt_validator,
         _library_sync: library_sync,
-        _event_bus: event_bus,
+        _event_publisher: event_publisher,
+        _event_consumer: event_consumer,
         config: config_arc,
         _sync_trigger: sync_tx,
     })