[world-vercel] Honor WORKFLOW_NODE_HTTP on the queue transport (#4044)

* fix(world-vercel): honor WORKFLOW_NODE_HTTP on the queue transport

getQueueDispatcher was the one dispatcher getter that ignored the flag. The
reasoning was that `undefined` cannot move the queue client onto node:http
(QueueClient takes a dispatcher and no fetch override), so returning it would
only drop this package's pool tuning and fall back to undici's global agent.

That misses what the flag is actually for. The deployments that need it are the
ones where the undici copy *this package bundles* is unusable, and `undefined`
does move the request off that copy: global fetch dispatches on the runtime's
own undici instead. On such a deployment every other request survives while the
queue client keeps dispatching through the broken copy, and an
acknowledgeMessage that never resolves means the message is redelivered for as
long as the platform keeps killing the invocation holding it.

Losing pool tuning is the correct trade under a flag whose premise is that the
bundled undici is not usable here. An explicit config.dispatcher still wins.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

* docs: correct the queue-send note for WORKFLOW_NODE_HTTP

The queue client is a partial exception to the flag, not a full one: it cannot
move to node:http, but it does honor the flag by dispatching through the
runtime's own copy of the HTTP client library instead of the copy the World
bundles. That distinction is the whole point when the bundled copy is what does
not work.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>