[BUG] Subscription streaming abort is completely disabled - in-flight queries cannot be cancelled #709

Describe the bug

In src/handlers/subscribe-message-handler.ts, the entire AbortController is commented out:

// private readonly abortController: AbortController
public abort(): void {
  //this.abortController.abort()  ← no-op
}

The class implements IAbortable but abort() does nothing. When a client disconnects mid-subscription (while streaming thousands of historical events), the query continues running to completion, holding a DB connection and wasting CPU/memory.

Expected behavior
Aborting a subscription should cancel in-flight streaming queries.

System: Linux, Docker