feat: add SQLite and PostgreSQL event queue adapters with migrations

crates/adapters/postgres-event-queue/migrations/0100_event_queue.sql

@@ -0,0 +1,13 @@
+CREATE TABLE IF NOT EXISTS event_queue (
+    id              BIGSERIAL    PRIMARY KEY,
+    event_type      TEXT         NOT NULL,
+    payload         TEXT         NOT NULL,
+    status          TEXT         NOT NULL DEFAULT 'pending',
+    attempts        INTEGER      NOT NULL DEFAULT 0,
+    created_at      TIMESTAMPTZ  NOT NULL DEFAULT NOW(),
+    next_attempt_at TIMESTAMPTZ  NOT NULL DEFAULT NOW(),
+    last_error      TEXT
+);
+
+CREATE INDEX IF NOT EXISTS idx_event_queue_poll
+    ON event_queue (status, next_attempt_at);