Start Equipment Issue Conversation Route

"File an issue on {label_id}" -- opens the SAME Issues intake conversation POST /api/issues/intake/converse continues (a plain conversation_id, matching that route's own contract exactly), seeded with the equipment context card and Rooster's opening line via intake_service.open_conversation's equipment_label_id hook. Lives here, not in app/modules/issues/routes.py, so U6 never has to touch a file another active build unit owns for anything beyond the one hook call already made in intake_service.py itself.