Share support conversation with organization

Make a conversation and its entire history readable by every organization member. Only its creator can share it. There is no customer operation to make it private again. Repeating this action leaves it shared. Accepts no body or an empty JSON object. Requires support.write and a user token. Organization API keys cannot call this operation. Uses customer permissions, with no operator or staff bypass. New mutations require rollout-agent-access-writes and allow-public-agent-writes to be enabled. Pausing writes leaves history and downloads available. Known IDs resolve their own organization; organizationId can require a specific tenant. Creation defaults to the saved organization.