Send a manual publisher dispatch

Admin-triggered "send now" for one or more dispatch-ready articles belonging to a team; enqueues a single publisher-order-send job for the whole selection, which the publisher receives as ONE thread carrying a message per article. use_resend routes a test send through Resend instead of Front and requires recipient_override: it applies to test sends only, so passing it without an override is rejected rather than ignored — a real dispatch always goes through Front. sender_override sets that test send's From; it requires both recipient_override and use_resend (a Front message is sent by the channel, whose From is not ours to set) and must be on the verified sending domain.