Document LISTEN/NOTIFY support for Postgres connections

Add documentation section covering the listen/notify API including
subscribe, unsubscribe, notify, and notification retrieval methods.
Includes note about using dedicated connections outside connection pools.

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Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: mcraveiro

docs/postgres.md

@@ -64,6 +64,8 @@ const auto minors = query(conn);
 
 PostgreSQL provides a simple publish-subscribe mechanism through `LISTEN` and `NOTIFY` commands. This allows database clients to receive real-time notifications when events occur, without polling. Any client can send a notification to a channel, and all clients listening on that channel will receive it asynchronously.
 
+> **Note:** You should use a dedicated connection for LISTEN/NOTIFY, separate from your main database activity and outside any connection pool. This is because the listening connection must remain open and persistent to receive notifications, and connection pools typically recycle connections which would lose the LISTEN state.
+
 ### API
 
 The `Connection` class provides the following methods for listen/notify: