docs(publishing): spec for #37449 push publish queue stall and Scheduled label

[hassandotcms]

Spec only (PR 1 of 2) for #37449.

Two sender-side Push Publishing defects:

1. An endpoint that does not answer connection attempts blocks the publisher, and every bundle pushed after it waits.
2. A bundle pushed for "now" is shown as Scheduled with the date its assets were added to the draft, until the publisher picks it up.

Proposed fix: a connect timeout on the publisher's HTTP client, per-bundle error isolation in the queue job, and reporting a due-but-waiting bundle as BUNDLE_REQUESTED instead of SCHEDULED in the v1 API.

Please review specs/37449-publishing-queue-dead-endpoint/spec.md. On approval, planning and implementation follow in PR 2.

This PR fixes: #37449