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/adapters/event-publisher/Cargo.toml

@@ -8,3 +8,7 @@ domain = { workspace = true }
 async-trait = { workspace = true }
 tokio = { workspace = true }
 tracing = { workspace = true }
+sqlx = { workspace = true, features = ["sqlite"] }
+serde = { workspace = true }
+serde_json = { workspace = true }
+chrono = { workspace = true }